Enero

Mass loss dominates stars on the asymptotic giant branch (AGB). Circumstellar shells of enriched material, fed by the mass loss, reprocess stellar light resulting in cool and luminous stars with ample emission longward of optical. As a result, ultraviolet and X-ray emission are not expected from AGB stars, but can originate from binary companions. Taking advantage of the nearly all-sky UV surveying capabilities of the Galaxy Evolution Explorer (GALEX), we have now established that most, if not all, AGB stars do emit in the UV. The origin of the UV emission is unclear; evidence exists for binary origins in some stars and intrinsic origins (photospheric, chromospheric and/or wind shocks) in others. I will review the UV properties of AGB stars and consider the evidence for binary and intrinsic origins.

Understanding the observations of dynamical tracers and the trajectories of lensed photons at galactic scales within the context of General Relativity (GR) requires the introduction of a hypothetical dark matter dominant component. The onset of these gravitational anomalies, where the Schwarzschild solution no longer describes observations, closely corresponds to regions where accelerations drop below the characteristic a0 acceleration of MOND, which occur at a well-established mass-dependent radial distance, Rc ∝ (GM/a0)1/2. At cosmological scales, inferred dynamics are also inconsistent with GR and the observed distribution of mass. The current accelerated expansion rate requires the introduction of a hypothetical dark energy dominant component. We here show that for a Schwarzschild metric at galactic scales, the scalar curvature, K, multiplied by (r4/M) at the critical MOND transition radius, r = Rc, has an invariant value of κB = K(r4/M) = 28Ga0/c4. Further, assuming this condition holds for r > Rc, is consistent with the full space-time which under GR corresponds to a dominant isothermal dark matter halo, to within observational precision at galactic level. For an FLRW metric, this same constant bounding curvature condition yields for a spatially flat space-time a cosmic expansion history which agrees with the ΛCDM empirical fit for recent epochs, and which similarly tends asymptotically to a de Sitter solution. Thus, a simple covariant purely geometric condition identifies the low-acceleration regime of observed gravitational anomalies, and can be used to guide the development of extended gravity theories at both galactic and cosmological scales

Febrero

The interpretation of polarization of protoplanetary disks at millimeter wavelengths has been dramatically changing. As a direct extension of polarization in star-forming regions, it has been thought that non-spherical dust grains aligned with magnetic fields would produce the intrinsic polarization in protoplanetary disks as well. However, it is pointed out that dust scattering can also produce polarization. Furthermore, even the direction of the alignment might not be determined by magnetic fields but by radiation fields. Recent ALMA observations have shown that both of the theories are at work in protoplanetary disks. Furthermore, the scattering-induced polarization suggests that grain size is not as large as millimeter but 100 micron, which is a crucial constraint on planet formation. I will review these recent theoretical and observational developments of millimeter-wave polarization in protoplanetary disks and discuss what we can learn from the polarization observations.

Warps or inclination changes as a function of radius have often been invoked to explain protoplanetary disk observations. Well characterised examples can inform on the origin of such warps, on their role in disk evolution, and may allow for new probes of physical conditions. In transition disks, the separation of the inner and outer disks by a radial gap allows firm constraints on warp geometry. There are now 4 examples of sharply warped transition disks, in which the outer disk is directly exposed to stellar light. In a couple of examples the temperature drop of the gas under the shadowed regions has been detected. Along with a description of the known warped systems, I will present a diagnostic of the outer disk mass based on the cooling timescale of the shadowed gas.

When a binary stellar system ventures too close to the supermassive black hole that resides at the center of every galaxy, the intense tidal field due to the latter can split up the binary. In a typical encounter, one of the stars becomes bound to the central black hole while the other is ejected out of the system with a kick velocity of the order of ~ 1000 km/s. In this talk, I will review a proposed model in which this mechanism can naturally account for two peculiar stellar populations in our galaxy: the S-stars at the galactic center and the hypervelocity starts in the galactic halo. Finally, I will present the outcome of recent general relativistic, numerical simulations of binary tidal breakups that systematically explore the vast parameter space that characterizes these encounters.

In this talk we will show you a study on the detectability of the emission associated with the Active Galactic Nuclei (AGN) dusty structure at sub-mm wavelengths in the era of ALMA. We hack this issue with a theoretical and observational approach considering three typical ALMA frequencies/wavelenghts (100GHz/3000μm, 353GHz/850μm, 666 GHz/450 μm). Theoretically, we use the Clumpy models from Nenkova et al. together with the mid-infrared to X-ray and the radio fundamental plane scaling relations. The latter scaling relation was included since a no negligible contribution at sub-mm wavelength may come from synchrotron emission of the AGN radio jets. The theoretical approach results in the more likely detection of big and dense dusty tori at the highest ALMA frequency (666 GHz/450 μm). Observationally, we use four prototypical AGN: NGC 1052, NGC 1068, NGC 3516, and IZw1, with radio, sub-millimeter, and mid-IR available data. After performing the mid-IR and radio spectrum fitting alone, we combined and extrapolated both fits in order to compare the extrapolation of both torus and jet contributors at sub-mm wavelengths. Our observational results are consistent with our theoretical results. The most promising candidate to detect the torus is the QSO IZw1, although it cannot be resolved due to its large distance. In order to explore the detection of a torus at sub-mm wavelengths, we suggest to perform a multifrequency SED analysis including also radio data.

Marzo

I will show the on-going analysis of NaCo/VLT data (Ks band polarimetry) of Sz91, a young (~2 Myr), transitional disk around an M1 star located in the Lupus III star-forming region. This object has one of the largest inner cavity observed in a disk around a T Tauri star (~100 au; Canovas, Schreiber et al. 2015) estimated from ALMA. The mm-size grains are concentrated in a narrow (~44 au width), ring-like structure. The micron-sized dust grains probed by our near-IR observations with NaCo lie inwards of the mm ring: a clear example of dust filtering. Our preliminary results suggest that the dust grains responsible for the polarized emission are porous (>60%), small (< 3 microns), silicate grains. With our new L-band observations (also acquired by our group), we are able to rule out the presence of very massive giant planets inside the cavity. I will also present the work in progress in the search for sub-mm cold cores that can harbor pre- and proto-BDs candidates in LDN1589, one of the most active star-forming clouds in the Lambda Ori Star-forming region. For this, we carried out 870-micron continuum observations of the dark cloud using APEX/LABOCA bolometer array. We have detected a few potential candidates (with S/N >= 4) of cold cores in the data. I’m currently doing the crossmatch of the detections with catalogs at different wavelengths in order to characterize the spectral energy distribution of the detected sources and to estimate their properties (e.g. bolometric luminosity) to discriminate if these are indeed pre- and proto-BDs. With this result at hand, we plan to propose sensitive ALMA observations to study dynamic signatures of the cores to confirm their sub-stellar origin.

Wolf-Rayet (WR) stars are related to some of the most exotic and interesting astronomical objects in the Universe, e.g. the most massive stars, binaries, supernova explosions, compact objects, Gamma Ray Bursts and gravitational waves. We here report the detection of seven new WR star locations in M81 using the Multi-Object Spectrograph of the OSIRIS instrument at the 10.4-m Gran Telescopio Canarias. In this work, we analyse the entire sample of 21 spectra to specifically identify spectra that correspond to individual WR stars of one of the known sub-types. For this purpose, we explore a variety of independent methods of classification and analysis. We find 18 of our 21 detections are associated to individual stars of sub-types WNL, WNE, WCE and transitional WN/C. Our study makes M81 the farthest galaxy with individual WRs reported, thus providing a new environment for testing the massive star evolutionary models.

Star formation is a complex process that can occur over a wide range of scales. To better understand this process it is important to study the stellar initial mass function (IMF) and the kinematics of stellar groups. An excellent laboratory to carry out this kind of studies is 25 Orionis (25 Ori). Combining new deep optical photometry from DECam with optical and NIR data from the literature, we selected 1687 member candidates of 25 Ori. With this sample we derived the system IMF of 25 Ori from 12 Mjup to 13.1 Msun, which is one of the few IMFs across the whole mass range of a stellar group. The resultant system IMF is well-described by a two-part power-law function and by a tapered power-law form. We also report its best lognormal parameterization. This system IMF do not present significant variations within a radius of about 7 pc, which indicates that the substellar and stellar objects in 25 Ori do not have any preferential spatial distribution. We compared the reported system IMF as well as the substellar/stellar ratio with those of a large diversity of stellar populations and did not find significant discrepancies, which strongly supports the hypothesis that the star formation mechanism is largely insensitive to environmental conditions. Also, I present the current status of a spectroscopic survey to confirm the membership of each candidate using several world-wide facilities (GTC/OSIRIS, SDSS-III/BOSS, MMT/Hectospec, SDSS-IV/APOGEE-2 and OAN-SPM/MES). So far the survey is 75% complete and we have confirmed 530 members. With this sample of members we estimated the parameters of 25 Ori (mean values of distance, visual extinction, age, radial velocity and proper motion as well as the velocity dispersion, total mass and stellar density). Using these parameters we found that 25 Ori is a dynamically young group that is gravitationally unbound. (These are the main results of my PhD thesis project)

Photodissociation bubbles are common features in the interstellar medium. They can be easily detected as ring-like structures in line emission maps tracing either neutral atomic or molecular hydrogen. One particularly clear case is in the $\lambda$-Ori region, which exhibits a quite symmetric, 20 pc radius ring that has been previously interpreted as to be the result of the expansion of a supernova explosion between ~1-2 Myr ago. Recently, high precision proper motions of stars in this region became available through the second data release of Gaia, which showed that the projected velocity vectors of $\lambda$-Ori stars tend clearly to point away from the center of the ring/bubble, as could be expected for an open cluster that it is breaking apart. Moreover, the data suggest that stars located farther from the center of the ring/bubble have faster (or larger) proper motions.This lead us to propose a different scenario for the formation of the $\lambda$-Ori bubble and its proper motions: In the present contribution we used numerical simulations to show that, while at the beginning, stellar clusters are formed in a collapsing environment and the stars are drawn to each other due to the gravity of the cloud, later the feedback from the newborn massive stars in these clusters expels the gas from the center, creating a cavity and moving the potential well away from the center of collapse. Since neither the formed shells nor the parental clouds are symmetric, a net force pulling out the stars is present, accelerating the stars towards the edges of the cavity. In this way, we propose that gravity from the expelled gas appears to be the crucial mechanism producing unbound clusters that expand away from their formation center. This mechanism has not been considered before, mainly because in previous simplified models the gravitational potential was usually one of an empty, homogeneous sphere, which is constant, and thus no net force is expected to act over the clusters embedded in a shell structure.

Star formation is the defining process in the evolution of galaxies. Our present understanding of star formation has primarily been informed by low-mass stars in nearby clouds, but these nearby regions do not reflect typical conditions over the history of the universe. The denser and more crowded regions that represent our own origins exist within our Galaxy, and ALMA allows us to explore these regions in ways previously impossible. I will show that high-density regions preferentially form clusters over isolated stars. In these dense, clustered regions, the stellar initial mass function (IMF) is governed by feedback from high-mass stars, which we demonstrate using ALMA to measure gas properties and identify individual protostars. Protostar-counting measurements provide tests of star formation theories, and they show evidence that star formation density thresholds vary with environment. These measurements can be repeated throughout the Galaxy to provide strong constraints on the formation of the IMF, which will be achieved by the recently-begun ALMA-IMF large program.

Abril

Giant radio galaxies (GRG) are defined as those active galactic nuclei (AGN) whose radio morphology show linear extended emission above 0.7 Mpc. The lobes in these galaxies can be as old as 10^8 years, whereas the AGN activity can be reactivated within 10^4-8 yrs, thus GRG are perfect laboratories to study AGN evolution and restarted activity. The usual way to find restarting activity is through the radio morphology, where different phases of nuclear activity can be observed in the same dataset. However, we might be missing a fraction of restarting activity in galaxies because we are not able to detect the earliest phase where the new jets have recently formed and are not visible in the radio band. In this seminar I will focus on two cases of restarted activity on early phases, namely PBC J2333.9-2343 and Mark 1498. These sources were selected on a hard X-ray basis and we performed multiwavelength analyses in order to gain information of different emitting regions and to have the most comprehensive view of their nuclei.

In many astrophysical systems, perturbers embedded in gaseous disk migrate due to the angular momentum transfer with the disk (e.g., protoplanets, black holes, globular clusters). I will discuss the different regimes that arise in the problem of the interaction between a gravitational body and a gaseous disk, for both prograde and retrograde orbits. Then, we will focus on the linear case, and compare the migration and circularization rates derived in the local approximation with those found in numerical simulations. We will discuss under what conditions the local approximation provides accurate estimates.

Mayo

We present multi-object spectroscopic observations of 23 globular cluster candidates (GCCs) in the prototypical megamaser galaxy NGC 4258, carried out with the OSIRIS instrument at the 10.4 m Gran Telescopio Canarias. The candidates have been selected based on the (u* - i') versus (i' - Ks) diagram, in the first application of the \uiks\ method to a spiral galaxy. In the spectroscopy presented here, 70% of the candidates are confirmed as globular clusters. Our results validate the efficiency of the \uiks\ method in the sparser GC systems of spirals, and given the downward correction to the total number of GCs, the agreement of the galaxy with the correlations between black hole mass, and total number and mass of GCs is actually improved. We find that the metal-poor GCs co-rotate with the HI disk, even at large galactocentric distances. The ratio of rotation to velocity dispersion V/sigma of the system is ~ 1, consistent with the highly turbulent, rotating disks at z>=2 that constitute nowadays the favored environment for the formation of globular clusters. This system could be a z = 0 relic of this process.

Magnectic fields are known to be extremely relevant at various stages of stellar evolution. Indeed, several investigations have focused on the role of those fields during stellar formation (e.g. molecular clouds) and in evolved massive stars ( e.g. SN). The detection and analysis of magnetism in the short period (~10,000 yrs) corresponding to the advanced evolutive phase of intermediate mass stars, namely post-AGB and Planetary Nebulae, is less known. I will present a review of the investigations realised so far, with a focus on the most recent observational and theoretical results. In order to better tackle this issue, we also formed a group dedicated to polarization studies and composed of several researchers from various national institutions. I will then present the different activities ( i.e. instrumentations and observations) of the group.

In this talk I will review the method of estimation of tidal deformabilities of compact stars and present results for pure hadronic as well as hybrid stars that include the mass twins case. Then I will discuss the impact of the nuclear symmetry energy in the determination of the compact star radius. In particular, the recent detection of gravitational radiation from the GW170817 event shed light on the properties of the neutron star equation of state (EoS), thus comprising both the study of the symmetry energy and stellar radius. Furthermore, I shall address the question of the possibility of a universal symmetry energy contribution to the neutron star equation of state under restricted Direct Urca cooling. When these two aspects are combined, powerful predictions for thestiffness of the neutron star EoS are obtained. Furthermore, I will focus on the case of mass twin compact stars, hybrid compact stars with approximately the same masses but different radii.To qualify the above, I will show a recent developed EoS that features of a color superconducting chiral quark model with nonlocal, covariantinteractions bearing density dependent vector meson coupling and a density-dependent bag pressure. This model allows for a scenario where thecompact stars of the GW170817 event are either both hadronic, both hybrid, or simultaneously hadronic and hybrid configurations.

Diverse numerical and observational evidence suggests that star-forming molecular clouds (MCs) may be in a process of global hierarchical contraction (GHC). As originally proposed by Hoyle (1953), in such a regime, a sequential destabilization of successively smaller masses should occur, leading to fragmentation of the cloud and ultimately to the formation of stellar-mass objects, when the equation of state diverts from isothermal. Early objections to the global gravitational contraction of MCs do not necessarily hold in the light of our modern understanding of turbulence and the structure of MCs. In this context, I discuss how the HGC mechanism implies a nearly pressureless collapse of mMCs and an initial acceleration of the star formation activity. These features naturally explain the ubiquitous formation of filamentary structures that funnel material to so-called "hubs", the observed morphology of the magnetic field around the filaments, the scattered nature of low-mass star-forming regions, the observed SFR-mass relations at both the local (cloud) level and the global (galactic) level, and the structure of the embedded stellar associations, such as their fractal structure and the observed radial mass and age gradients, as well as their stellar-age histograms.

I will present recent observational and modelling results that tackle the following important issues on star-cluster formation: i) The diversity of massive, cluster forming clouds, and a possible origin for it. ii) Evidence for gas accretion from GMC ($\sim 50$ pc) to disk ($< 1000$ au) scales. iii) The first censuses of the stellar populations in formation, i.e., YSO counting in massive protocluster clouds. iv) The effects of feedback from massive YSOs on their natal cores and clumps.

The motivation for a pseudo-complex General Relativity will be given and the main structure will be resumed. Simulations of a thin accretion disk are presented and compared to the observation of the black hole in M87 by the EHT collaboration. Some problems are discussed.

Septiembre

Dust scattering can be a very important opacity source in protoplanetary disks observed at radio wavelengths with ALMA and VLA. However, scattering is usually neglected in analysis of multi-wavelength observations because it increases the complexity of Monte Carlo simulations and is time consuming. In this talk, I present an analytical solution of the emergent intensity of a vertically isothermal face-on disk, taking into account the scattering in the radiative transfer equation. The emergent intensity with scattering modifies the spectral indices compared with that of the non-scattering emission. The shape of the spectral energy distribution is also modified, depending on the disk inclination in the plane of the sky which increases with the optical depth. Finally, we used the scattering effects to give an alternative explanation to the observed excess emission reported at a wavelength of 7 mm in several disks. These results were recently implemented to explain the radial dust distribution in the HL Tau disk.

Orion is the region of massive star formation closest to the Sun and in consequence it has been studied in detail. I will present three recent results from the IRyA group on this region. The first one is the ultraprecise determination of the distance to Orion using VLBI observations of stars with non-thermal emission. The second result is a study of the kinematics of the stars with either termal or non-thermal emission. Finally, we will focus on the extraordinary “explosion” that seems to have taken place in the Orion BN/KL region. Not only the molecular gas but also several stars are receding from a point in common with velocities of hundreds of km/s for the gas and of tens of km/s for the stars. We will present the most recent data on the proper motion of the stars and discuss the models that have been proposed to explain this phenomenon.

Octubre

The dust component affects the measurements of galaxy properties since dust absorbs and re-emits the starlight from the UV and the optical radiation. The latter process enables the prediction of the emission of radiation at infrared-submillimeter-radio wavelengths, by fitting evolutionary stellar population synthesis (SPS) models to observed UV-optical-NIR observations and assuming a dust emission model. Nevertheless, the predictions depend on the choice of the SPS model, e.g., Bruzual and Charlot (2003), or the Maraston (2005) models. This is mainly due to the different treatments of the thermally pulsing asymptotic giant branch (TP-AGB) phase of stellar evolution. Comparisons of the SPS models with resolved (e.g., pixel-by-pixel) observations (at optical and NIR wavelengths) can be used to discriminate between models. We will show the results of these comparisons to a sample of nearby disk galaxies.

Enero

The latest hydrodynamic cosmological simulations (e.g., EAGLE, Illustris, IllustrisTNG) have been able to produce reasonably realistic populations of galaxies by tracking the evolution of dark matter, gas, stars, and black holes over a cosmological volume "representative" of the large-scale density field. However, such increasingly sophisticated cosmological simulations require equally sophisticated analysis tools. In this talk, I will first discuss how to connect galaxies in large cosmological simulations across cosmic time, which results in data structures known as merger trees. Then I will examine three essential and increasingly complex applications of the merger trees: (1) measuring the merger rate of galaxies, (2) finding out how galaxies acquire their stellar mass, and (3) investigating the impact of mergers on galaxy morphology.

Star formation is one of the key mechanisms driving the formation and the evolution of galaxies across cosmic times. The physical properties and dynamics of the molecular gas influence the star formation efficiency, and therefore play a role in the growth of galaxies. Looking at large scales is therefore essential to understand the multi-scale physics of star formation. The environment may play a role in star formation. In particular, recent studies suggest that AGN can regulate the gas accretion and thus slow down star formation (negative feedback). However, evidence of AGN positive feedback is also invoked in a few radio galaxies (eg. Centaurus A, Minkowski's Object). I will present different studies of the northern filaments of Centaurus A at different resolutions. These filaments extend on scales up to 15 kpc, aligned with the radio-jet, and show evidence of recent star formation (Rejkuba et al. 2001). Along the radio jet, at the intersection of the radio jet and a HI shell (Schiminovich et al. 1994), CO emission has been detected with SEST in the shell (Charmandaris et al. 2000). We detect CO in a much larger area along the filaments with APEX, including outside the HI gas (Salomé Q et al. 2016a). Recently, we obtained ALMA observations along the filaments, at a resolution of ~20 pc (Salomé Q. et al. 2017). Such resolution enables to separate giant molecular without resolving them.

I give a summary of our project to explore the relationship between the total number of globular clusters, N_{GC}, and the mass of the central black hole, MBH, in spiral galaxies, and how it compares with that recently reported for elliptical galaxies. I present results for the globular cluster system of the Sbc galaxy NGC4258, from u*, g', i', r', and Ks data obtained with the Canada France Hawaii Telescope (CFHT). Thanks to water masers in a circumnuclear disk, the absolute distance to NGC 4258 has been derived directly by geometric means, and hence it has the most precisely measured extragalactic distance and supermassive black hole mass to date. The globular cluster (GC) candidate selection is based on the (u* - i') vs. (i'-Ks) diagram, which is a superb tool to distinguish GCs from foreground stars, background galaxies, and young stellar clusters, and hence can provide the best number counts of GCs from photometry alone, virtually free of contamination, even if the galaxy is not completely edge-on. We have thus increased to 6 the sample of spiral galaxies with measurements for both MBH and N_GC. NGC4258 has a specific frequency S_N=0.4±0.1 (random uncertainty), and it is consistent within 2 sigma with the N_GC vs. MBH correlation followed by elliptical galaxies. The Milky Way continues to be the only spiral that deviates significantly from the relation. Future work includes spectroscopic confirmation of cluster membership and hence validation of our method, and the study of the N_GC vs. MBH correlation in the remaining 8 northern spirals within 16 Mpc that have precise measurements of their BH masses, and for which we should finish collecting the required CFHT data in the coming months.

Febrero

I will present the tools developed by my student Andres Izquierdo to plug-in a variety of 3D analytical models to the radiative transfer code LIME. Then I will show our work in progress in the first two applications of these tools: 1) modelling ALMA observations of the massive YSO(s) in W33A, an object that we naively thought it was a massive disk in the pre-ALMA days, and that current data revealed is a multiple, complex system being fed by accretion filaments (burritos), 2) modelling of the effects of self-obscuration in the submillimeter appearance of class 0 disks, where we find that we can explain shallow (sub)mm spectral indices without the need to invoke grain growth, and reproduce recent resolved images of dark lanes (hamburguers) in class 0 YSOs when observed with the ~20 mas resolution provided by ALMA long-baseline observations.

I will present a short summary of the work I did during my PhD on velocity dispersions of molecular gas in nearby galaxies. Despite the fact that molecular gas in galaxies is the most essential ingredient for the star formation process, its thorough characterization has not yet been accomplished. On 0.5 kpc scales (the average spatial resolution of my work), the measured CO velocity dispersions have a mean value of ∼ 12 km/s. These values are higher than previously expected, and are comparable to those measured for neutral atomic gas. To investigate the origin of these large dispersions, a comparison between interferometric and single-dish line width measurements for NGC 4736 and NGC 5055 (at ∼ 0.5 kpc resolution) and for the neighboring Andromeda galaxy, M 31, (at ∼ 100 pc resolution) is presented. At the end I will shortly speak about future projects for outreach in Astronomy.

I will present the results of an radio-astrometric VLBI program (GOBELINS) aimed at measuring the trigonometric parallaxes of tens on young stars distributed over the nearest star-forming regions (Taurus, Ophiuchus, Perseus, Orion, and Serpens). These observations provide the distances to these YSOs to an accuracy of about one percent that surpasses previous (mostly indirect) determinations by one order of magnitude. Aside from improving our knowledge about the distribution of local star-forming regions, these results reveal (for the first time) the 3D structure of individual regions. For instance, Taurus is found to be about 30 pc deep, with different clouds/filaments located at different distances.

Extreme value theory (EVT) is a unique statistical discipline that offers techniques and models for describing the unusual rather than the usual. By definition, extreme values are scarce, meaning that estimates are often required for outcomes that are much greater than have already been observed. Extreme value theory provides a class of models to enable such extrapolation based upon asymptotic analysis of probability distributions. In this talk I will introduce you to the methodologies of EVT and will take you through the models used by the theory. I will discuss its advantages and disadvantages and conclude the talk by giving a demonstration of an application of the EVT to extreme solar flare events.

Marzo

Black holes are among the most spectacular predictions of Einstein’s theory of general relativity, and nowadays they lie at the forefront of theoretical physics and astronomy. In this talk, after providing a summary of the most important and intriguing properties of black holes, I will discuss recent work on the behavior of a collisionless kinetic gas under the influence of the gravitational potential of a Kerr black hole. Two regimes will be discussed. The first regime considers the case where the individual gas particles move on unbounded trajectories in which case the collection of particles describes an accretion process. The relevant parameters, such as the accretion and compression rates, are determined and the results are contrasted with those of the typical Bondi-Michel accretion model in the hydrodynamic case. The second regime focuses on the case where the gas particles are trapped in the gravitational potential and move on bounded trajectories. In this case, an interesting mixing phenomena seems to be taking place, which implies that although collisions between the gas particles are neglected in our model, the gas configuration settles down to a stationary, axisymmetric disk surrounding the black hole. This investigation which is performed in collaboration with my PhD student Paola Rioseco is partially motivated from the need of a thorough understanding for the behavior of matter in the vicinity of a supermassive black hole, such as Sagittarius A*, in view of upcoming observations of their shadows.

We want to explore what are the advantages and limitations of the fossil record method and show some results of the application of this technique using the MaNGA data. In the first part of this talk, we have post-processed two Milky Way-sized zoom-in Hydro simulations to create a set of mock observations to test the robustness of the fossil record inferences. In the second part, we explore the resolved star formation histories of 140 AGNs, 1,079 star-forming galaxies, 593 green valley galaxies and 961 quenched galaxies with the aim to reconstruct their evolutionary tracks along the main sequence diagram.

I will present radiation-magnetohydrodynamic simulations aimed at studying the evolution of molecular clouds (MCs) formed by diffuse converging flows in the presence of magnetic fields and massive-star ionization feedback. I will discuss how the magnetic field tends to enhance the star-formation activity by suppressing the dynamical instabilities that produce turbulence within MCs. This is an important but counterintuitive result since the common belief is that the magnetic field provide support to molecular clouds against its self-gravity, regulating thus the process of star formation. Finally, I will discuss the impact of supernova explosions and UV feedback in the final stages of the cloud evolution. Particularly, I will discuss the structure and expansion laws of HII regions in our highly structured MCs as well as the implications of our results for theoretical models.

Stellar bow shocks are the result of the supersonic interaction between a stellar wind and its environment. Some of these are "runaways": high-velocity stars that have been ejected from a star cluster. Others are "weather vanes", where it is the local interstellar medium itself that is moving, perhaps as the result of a champagne flow of ionized gas from a nearby H II region. We propose a new two-dimensional classification scheme for bow shapes, which is based on dimensionless geometric ratios that can be estimated from observational images. The two ratios are related to the flatness of the bow's apex, which we term planitude and the openness of its wings, which we term alatude. We calculate the inclination-dependent tracks on the planitude-alatude plane that are predicted by simple models for the bow shock shape. We also measure the shapes of bow shocks from three different observational datasets: mid-infrared arcs around hot main-sequence stars, far-infrared arcs around luminous cool stars, and emission-line arcs around proplyds and other young stars in the Orion Nebula. Clear differences are found between the different datasets in their distributions on the planitude-alatude plane, which can be used to constrain the physics of the bow shock interaction and emission mechanisms in the different classes of object.

Abril

Eta Car is one of the most massive, and intriguing, Luminous Blue Variables known. In its core resides a binary with a 5.54 years orbital period. Visible, infrared, and X-ray observations suggest that the primary star exhibits a very dense wind with a terminal velocity of about 400 km/s, while the secondary shows a much faster and less dense wind with a terminal velocity of 3000 km/s. The wind-wind collision zone at the core of Eta Car is thus a complex region that deserves a detailed study to understand the effect of the binary interaction in the evolution of the system. In this talk we will perform a review of the basic principles of the optical/near-infrared interferometry, together with our unique imaging campaign with VLTI - GRAVITY of the Eta Car's core. The superb quality of our interferometric data, together with state-of-the-art image reconstruction techniques, allowed us to obtain, with milliarcsecond resolution, continuum and chromatic images across the BrG and HeI lines in the Eta Car K-band spectrum (R~4000). These new data together with models of the primary wind of Eta Car has letting us to characterize the spatial distribution of the dust and gas in the inner 40 AU wind-wind collision zone of the target.

Dust in star forming region efficiently absorb the optical emission from stars inside them and, thus, many Young Stellar Objects will not be detected and studied by the Gaia satellite. Fortunately, these stars are often associated with radio emission, which may be used for astrometric studies. In this talk I will present recent results in this context. First, we have used archived Very Large Array (VLA) observations, spanned during the last 30 years, to measure the proper motion of ~100 YSOs in the ONC core, which gave us an interesting view of the stellar kinematics of this region and select stars with peculiar proper motions. However, the angular resolution of the VLA is much smaller than that provided by the Gaia telescope, but this is not the case of the Very Long Baseline Array (VLBA). VLBA has been used during the last decade to determine distances to several near and far galactic star forming regions with precisions comparable and, in some cases, better than those that the Gaia satellite will provide. In the second part of my talk, I will focus on recent results of distance measurements, using observation with the VLBA, to nearby (<1 kpc) star forming regions: Monoceros R2, LkH\alpha 101 and IRAS 16293-2422 (in Ophiuchus).

By adopting the empirical estimates of the Helium enhancement (delta Y) between consecutive stellar generations in a sample Galactic Globular Clusters, as well as the present mass ratio between consequtive stellar generations (M(j-1)G=M(j)G) and the present total mass of Galactic Globular Clusters (MGC), we uniquely constraint the star formation efficiency (epsilon) of each stellar generation in these stellar systems. In our approach, the star formation efficiency is the central factor that links the stellar generations as it defines both the mass in stars in each generation and the remaining mass available for further star formation, fixing also the amount of matter required to contaminate the next stellar generation. In this way, epsilon is here shown to be fully defined by the He enhancement between successive generations in a GC. Our approach allows also for the evolution of clusters and thus considers the possible loss of stars through evaporation or tidal interactions. We also show that globular clusters fit well within a deltaY vs M(j-1)G/M(j)G diagram which indicates three different evolutionary paths. The central one is for clusters that have not loss stars, through evaporation or tidal interactions, from either of their stellar generations, and thus their present MGC value is identical to the total amount of low mass stars (M < = 1 Msol) that resulted from each stellar generation. Other possible evolutions imply either the loss of first generation stars or the combination of a low star formation efficiency in secondary stellar generations and/or the loss of stars from the next generation. From these considerations we derive a lower limit to the mass (Mtot) of the individual primordial clouds that gave origin to each of the globular clusters in our sample.

In this talk I will discuss a Primitive Variable Recovery Scheme (PVRS) to solve any system of coupled differential conservative equations. This method obtains directly the primitive variables applying the chain rule to the time term of the conservative equations. With this, a traditional finite volume method for the flux is applied in order avoid violation of both, the entropy and "Rankine-Hugoniot" jump conditions. The time evolution is then computed using a forward finite difference scheme. This numerical technique evades the recovery of the primitive vector by solving an algebraic system of equations as it is often used and so, it generalises standard techniques to solve these kind of coupled systems. Applications to special relativistic hydrodynamics including in some cases a fixed background curved space-time will be discussed. I will also talk about the development of aztekas.org a free GPL'd code for solving any set of coupled conservative equations.

The High Altitude Water Cherenkov Observatory (HAWC) is a facility designed to detect extensive air showers produced by very-high-energy gamma rays and cosmic rays interacting with our atmosphere. It is located in the Pico de Orizaba National Park in Puebla, México. Since its inauguration in April 2005, the HAWC observatory has been operating almost continuously detecting gamma rays coming from galactic and extragalactic sources. In this talk an overview of the most relevant scientific results from the HAWC Collaboration will be given.

Mayo

Using the VLA to reach sensitivities of 3–10 μJy/beam, we found that radio continuum sources are more commonly found towards high-mass protostars than previously expected. Many of these radio continuum sources are weak (on the order of < 1 mJy) and have morphologies and other observational parameters that resemble collimated ionized jets, which is in general agreement with recent theoretical models developed exclusively for high-mass protostars based on core accretion. We are building a sample of ~20 high-mass protostars with comprehensive observations from radio to mid-IR using VLA, SOFIA and ancillary data to test and refine these new protostar formation models that predict both the morphology and spectral energy distribution. I will present results showing that extending the infrared SEDs to radio wavelengths is effective in breaking degeneracies in the fitted model parameters.

Dwarf spheroidal galaxies are dark matter dominated. Therefore, they are ideal to test any dark matter model. In this colloquium I will talk about my previous work on stellar substructures in dwarf spheroidal galaxies and how important they are to constrain dark matter models. I will continue to present our newly discovered stellar substructures in Sextans, Carina, Leo I and Leo II. Finally, I will present my current and future work.

Recently commissioned telescopes and instruments (e.g., Subaru, GPI, VLA, ALMA, EVLA) are now finally able to resolve the protoplanetary disk down to the AU scale, and a rich variety of disk features have been revealed: gaps, large scale disk asymmetry, and spiral arms. To confront these observations, theoretical models need to be developed so that we can use observations to constrain the physics of disk structure and planet formation. In the talk, I will summarize our recent progress on planet-disk interaction study, focusing on explaining the observed spirals and how a single planet can lead to multiple gaps. To directly find young planets, I will argue that disks around these forming planets, so-called circumplanetary disks, could be the key and we may have already found some circumplanetary disk candidates.

High-mass stars are known to be formed within massive and dense clumps with masses of typically 1e3 Msol and sizes of 1 pc . However, the way in which the high-mass are formed is still an open question. Here we discuss ALMA observations of a handful of massive and dense clumps in early stages of evolution, previous to the formation of high-mass stars, revealing the spatial distribution and kinematics of the small scale structures, or cores, within the clumps. We find that the Core Mass Function is strikingly different from that of the IMF.

Planetary systems have long been known to form from the gas and dust of circumstellar disks. In recent years, the transformational observations provided by ALMA have increased and shaped our understanding of these systems. However, the study of several important physical processes, such as dust growth or gas photoionization and dispersal, requires observations across a wider range of wavelengths than what ALMA can probe. In this talk I will show the combined results of VLA and ALMA observations toward two protoplanetary disks that show signs of ongoing planetary formation: GM Aur and HD 169142. In both disks, the ALMA and VLA observations revealed the presence of multiple rings and gaps, likely produced by the dynamical interaction between the disks and young planets in them. At the same time, both sources show substantial free-free emission associated with ionized gas. In the case of GM Aur, we resolve this emission and see that it is associated with a radio jet and a photoionized disk, providing new insights into disk photoevaporation and dispersal.

Interplanetary scintillation (IPS) manifests itself as a variation in the radio signal received from a distant, compact radio source on the sky as the radio waves traverse the interplanetary medium due to density inhomogeneities in the outflowing plasma. IPS allows us to infer the speed and density of the plasma. There are two types of techniques that provide IPS solar wind speed determinations in the heliosphere: Single-Station analysis (SSA) and multi-station Cross Correlation Function (CCF) analysis. In order to combine and complement solar wind speed observations, it is important to validate results and methodologies of the two techniques. We apply the SSA to previously-well studied European Incoherent SCATter (EISCAT) and Multi-Element Radio-Linked Interferometer Network (MERLIN) observations of IPS with well-known results using the CCF methodology in order to know the capabilities of the SSA to describe complex events and seeks to obtain improved parameter fits using the SSA of individual IPS spectra.

Scaling relations are the most powerful astrophysical tools to set constraints to the physical mechanisms of astronomical sources and to infer properties for objects where they cannot be accessed directly. We re-investigated one of these scaling relations using mostly NLSy1 and Sy1 (González-Martin 2018); the so-called X-ray variability plane (or mass-luminosity-timescale relation, McHardy et al. 2006). This relation links the power-spectral density (PSD) break frequency with the SMBH mass and the bolometric luminosity. We used all available XMM-Newton observations of a sample of 22 Sy1 and NLSy1 to study the PSD and spectra in short segments within each observation. This allows us to report for the first time that the PSD break frequency varies for each object, showing variations in 19 out of the 22 AGN analyzed. Our analysis of the variability plane confirms the relation between the break frequency and the SMBH mass and finds that the obscuration along the line of sight (or the variations on the obscuration using its standard deviation) is also a required parameter. The X-ray variability plane found by McHardy et al. (2006) is roughly recovered only when we use unobscured segments. We speculate then that the PSD shape is related with outflowing winds close to the accretion disk.

Junio

Observations at millimeter wavelengths and in IR scattered light have revealed numerous substructures in protoplanetary disks when observed at high spatial resolution. These substructures are of primordial importance as they might stop the dust radial migration onto the stars and concentrate efficiently dust particles, then yielding to the formation of planetary embryos. In this talk, I will present recent ALMA observations of two planetary disks around the Herbig stars HD 142527 and MWC 758. These disks are well-known for showing numerous outstanding features. They present dust asymmetries, with a small gas-to-dust ratio, that are thought to be ideal places to develop hydrodynamical instabilities (such as the streaming instability) yielding afterwards to gravitational collapse and planetary embryos formation. Additionally, the disks feature spirals observed with ALMA and previously detected with Subaru and the instrument Sphere of the VLT that might trace planets already formed. Planets with a mass larger than about 1 Jupiter mass are known to produce cavities and spirals in protoplanetary disks, that might be more visible than the planets themselves. However, other scenarios including perturbations by a stellar encounter, shadows cast by the inner regions of the disks, among others, will also be discussed.

Active galactic nuclei (AGN) are among the most exciting objects in the universe due to the large energy range covered by their spectrum from radio to gamma rays, which can be explained trough several physical components and processes. With the advent of large ground based telescopes like the 10.4m Gran Telescopio CANARIAS (GTM) and the mid-infrared camera CANARICAM, a better understanding of the nuclear dust in AGNs have been reached. In this talk I am going to present the results that we obtained from studying the mid-infrared emission in high luminosity AGNs. Additionally, I going to show some results of our progress work on the study of the silicate features in type 1 AGNs and our looking for optical obscured AGNs.

The Hubble (HST) and Spitzer telescopes were the first instruments to unveil the presence of rings and arcs around evolved low-mass stars (AGB stars, proto-PNe and PNe)in great detail. Since the mid-2000s it was suggested that these structures were ubiquitousaround evolved low-mass stars. We searched the complete archive of the HST and Spitzer to characterise these structures, study their physical properties and characterise their formationmechanisms. In this talk we present the observational results of our survey, the predictions of simple radiation-hydrodynamic simulations as well as the future of the project.

In this talk, I will present an analysis of newly discovered coherent structures in the L1688 region of Ophiuchus and the B18 region of Taurus. The structures are identified in a search of ammonia spectral cubes from the Green Bank Ammonia Survey (GAS; Friesen et al. 2017) alongside Herschel maps of thermal dust emission, looking for regions of high density and near-constant, almost-thermal, velocity dispersion. Eighteen coherent structures are revealed, twelve in L1688 and six in B18, each of which shows a sharp “transition to coherence” in velocity dispersion around its periphery. We call these structures “droplets,” owing to their small sizes and masses, as well as their gravitational unboundedness. To examine the droplets’ kinematics and internal structures, I will present a virial analysis and comparisons to a Bonnor-Ebert sphere, a logotrope, and previously observed starless cores. Lastly, by comparing to MHD simulations, I will investigate several potential formation mechanisms for droplets, and speculate on the role that droplets, and coherent structures more generally, may play in the process of star formation.

Julio

We use HII galaxies in a joint likelihood analysis with other complementary cosmic probes (Cosmic Microwave Background, Baryon Acoustic Oscillations) to trace the Hubble relation through most of cosmic history and thus obtain constraints for the Hubble constant and the parameter space of the Equation of State of Dark Energy, the putative causal agent behind the accelerated expansion of the Universe, which is today a most intriguing problem in physics. The cosmological constraints thus obtained, are in excellent agreement with those of a similar joint analysis using the well established Type Ia Supernovae Hubble expansion probe.

Septiembre

About 30% of disc galaxies in the local Universe present prominent stellar bars in their centers. This fraction of barred galaxies depends strongly on several physical properties of the galaxies, such as stellar mass, colour and overall morphology. In this talk I will give a short review of the role of the dark matter halo, the galactic spin and the gas content in the formation and evolution of stellar bars as predicted by theoretical studies, and I will provide observational results that can help to discriminate between different theoretical models.

Planetary nebulae, the descendants of low- and intermediate-mass stars, have characteristic onion-like ionization structure, with the highest ionization species closer to the central star. This is true for all planetary nebulae, but HuBi 1, which shows an inverted ionization inner shell. There is a reason for this oddity, the peculiar evolutionary path of its central star, which makes HuBi 1 the missing link of the population of cool C-rich central stars of planetary nebulae and explains many of their properties.

The study of the AGN accreting close to the Eddington limit (L/LEdd~1) has taken an important role, due to their potential use as standard candles for cosmological applications. With the purpose to understand the physics of extreme quasar, we perform a spectroscopic analysis of a sample of highly accreting quasars at high redshift (z~2–3). Our sample were observed with the OSIRIS spectrograph on the GTC 10.4 m telescope located at the Observatorio del Roque de los Muchachos in La Palma. The highly accreting quasars were identified using the 4D Eigenvector 1 formalism, which is able to organize type 1 quasars over a broad range of redshift and luminosity. The kinematic and physical properties of the broad line region have been derived by fitting the profiles of strong UV emission lines such as AlIII λ1860, SiIII]λ1892 and CIII]λ1909. We find that AlIIIλ1860 can be associated with a low-ionization virialized sub-system. xA sources show strong blueshifts in the high-ionization lines like in CIVλ1549, indicating a relation between the high Eddington ratios and the productions of outflows. The extreme radiative properties of highly accreting quasar make them prime candidates for maximum feedback effects on the host galaxy. The characterization of extreme quasar allow to assemble large samples of extreme quasars from the latest data releases of the SDSS, especially useful for deriving independent estimates of ΩM in the redshift range 1

In a collaboration of the ABACUS-CINVESTAV laboratory, the ESFM, the ININ and the Universidad Iberoamericana we have developed a database of stellar atmospheric models with the code CMFGEN (Hillier and Miller, 1998). The models were calculated in the cluster ABACUS of the ABACUS-CINVESTAV Applied Mathematics and High Performance Computing Laboratory and cover the region of massive main sequence stars. Currently the database has 40,000 models, our goal is to reach 75,000 models. Our research group has developed software tools for the administration of the database, queries under a search criteria, visualization of several spectra simultaneously and automatic adjustment of models. One of these tools is the FITspec program (Fierro et al. 2018), which performs a quantitative spectroscopic analysis based on the equivalent widths of He I, He II, and Balmer lines, reducing the time needed for the spectral analysis from months to hours, optimizing in this way the calculations. In addition to the description of the database, I will present partial results of the analysis of a sample of type O stars from the spectroscopic catalog of San Pedro Mártir.

Octubre

Standard cosmological models over predicts the number of small galaxies. Thus, a self-regulation of the star formation is commonly accepted, although is far from being observed and understood. Star formation and its self-regulation is a key process which the models oversimplify because of their limited resolution. If we want to understand the self-regulation of star formation, we need to study the resolved laws of star formation. I will present the results of the resolved main sequence of star formation on star forming clumps from a sample of 46 pair of galaxies, and 38 non interacting spirals. We found that the resolved main sequence of star formation is broken on kpc scales because the star formation is more centrally concentrated than the stellar mass. We also found that the clumps in the interacting galaxies have more SFR per stellar mass compared to the non interacting spirals. I will also present preliminary results on the analysis of the stellar populations of NGC 628 using MUSE data, and the code SINOPSIS. We compared the SFRs at the two most recent ages bins in different regions. I will show how we are able to characterize the self-regulation of the star formation between these two ages.

Noviembre

Massive stars impact their surroundings through strong winds, intense radiation fields, outbursts and supernova explosions. Their compact remnants are sources of X-rays and Cosmic Rays, which penetrate deep into molecular clouds affecting both temperature and chemistry. Ionizing radiation is a key feedback process for young stars, so I will first discuss the ionization-front instability to determine if and when it could produce pillars and globules in expanding HII regions. Then I will show results from some work we are doing on the stellar-wind bubble NGC 7635 and its X-ray and infrared emission. Finally I will show results from studying the time-dependent chemistry of molecular clouds when exposed to intense X-ray flares. Even a 10 or 20-year X-ray flare can change the chemistry of a cloud for thousands of years afterwards. We find that CO is destroyed much more rapidly than H2, providing a possible explanation for some of the CO-dark clouds that are found in extreme environments.

In old stellar systems, most of the matter returned to the ISM comes from AGB stars. We don't know exactly how it happens, because many different phenomena occur at the same time. Here, I will present recent observations we have taken of stellar winds. I hope to convince you that it is stellar pulsations that dictate mass loss from stars, while radiation pressure dictates how fast material leaves the star. In the process, I will touch on topics ranging from interstellar radiation to the evolution of planetary systems, and I will note the impact these results have on stellar evolution theory and modelling of stellar populations.

Infrared observations of nearby galaxies and the Milky Way show that there are two main sources of ISM dust: the winds of evolved stars and supernovae ejecta. However, the total dust contribution from evolved stars relative to supernovae, and how it changes with metallicity, is less certain. Infrared photometric and spectroscopic Spitzer Surveys of the Large and Small Magellanic Clouds (LMC, SMC): Surveying the Agents of Galaxy Evolution (SAGE) resulted in the discovery of thousands of evolved stars. Here, I will describe how the composition and quantity of dust produced by these stars depends on metallicity. I will also discuss how the mid-IR stellar populations of the Magellanic Clouds can be used as a template for potential observations with JWST, and how we have applied this to our observing programs of stellar populations Local Group galaxies and SN1987A with JWST.

In this talk, I will present theoretical results from both analytical and numerical models of the 1840s eruption of the massive star Eta Car, that resulted in the formation of a bipolar structure which is commonly known as the large "Homunculus nebula". During this event, the star expelled into the circumstellar material a total mass of ~10 Msol and released a total energy of E~ 10^(50) ergs over a very short time (< 5 yr). In the case of Eta Car, a brief explosion scenario provides a potential explanation for the behavior of the historical light curve of Eta Car a few years after the nineteenth century outburst, as well as some observed physycal properties of the nebula. Nonetheless, I show through numerical simulations that an explosion model for the 1840s major eruption of Eta Car is not able to account for the estimated age of the large Homunculus.

Dust is a key ingredient in many astrophysical processes. It is the catalyst for the formation of molecular hydrogen, and allows efficient cooling of collapsing cores leading to the formation of stars. Information about the astrophysical processes responsible for its growth and formation is imprinted in the dust in the form of mineralogy. Unlike gas, therefore, dust retains a memory of these processes for timescales up to ~1 Gyr.Dust is formed in the outflows of low-mass (1-8 Msun) evolved stars and also in the explosions of massive (>8 Msun) evolved stars. However, supernovae (SNe) reverse shocks also destroy significant amounts of dust. While the net contribution of dust from SNe is therefore highly uncertain, it is relatively easy to determine the total input from asymptotic giant branch (AGB) stars, which are numerous in present-day star-forming galaxies. Our group has identified AGB candidates in many nearby galaxies, and has used a grid of radiative transfer models to fit their spectral energy distributions in order to derive the total dust input to the interstellar medium (ISM). In this talk, I will summarise our findings and also advertise ongoing modelling and observational efforts related to dust in various environments as well as AGB stars in the Solar Neighbourhood.

Diciembre

Using the Newtonian CAFE MHD code to perform numerical resistive 2-3D MHD simulations, we have shown that jets with features of Type II spicules and cool coronal jets can be formed due to magnetic reconnection. To perform 2D simulations, as initial models we used two different magnetic configurations (i) a symmetric case, i.e. when the magnetic field strength of the two neighboring magnetic loops is equal and (ii) an asymmetric case when magnetic strength of loops is different. In the case (i), the excited jets rise vertically, whereas in the case of an asymmetric configuration (ii) the jet shows an inclination, which depends on the magnetic field strength ratio of the two loops and the distance between them. In the 3D simulation the magnetic configuration corresponds to a 3D potential magnetic field extrapolated from a dynamic realistic MHD simulation of solar photospheric magnetoconvection, which is mimicking quiet-Sun. We have found that the formation of the jet depends on the Lorentz force, which helps to accelerate the plasma upward. Analyzing various properties of the jet dynamics, we found that the structure shows Doppler shift, rotational and torsional motions. The morphology, the upward velocity coveting a range up to 130 km/s, and the timescale formation of the structure between 60 and 90 s, are similar to those expected for Type II spicules.

I will discuss a toy power-law model for the growth of black holes ingalaxies and their role in quenching. Galaxies while star-forming areassumed to exist at the centers of relatively undisturbed dark halos,and their stellar mass and radii are linked to halo properties viasimple relations. Central stellar density is assumed to correlatewith black hole mass. Quenching occurs when total energy emitted bythe black hole equals some total energy needed to heat the halo, whichis assumed to equal the gravitational binding energy of the halo gas. These assumptions matchthe observed distributions of star-forming and quenched galaxies in the R_e - M* and Sig_1 - M* planes from z ~ 3 to now. Animplication is that halos are a 2-parameter family that imprint theirproperties on the 2-D family of galaxies and that halos and the BH massesare connected through galaxy effective radii.

Enero

The Very Long Baseline Interferometry (VLBI) technique combines radio telescopes separated by thousand of kilometers to achieve the highest spatial resolutions in all of astronomy.
Motivated by the need of basic stellar parameters determinations such as distances, sizes, and masses, in the star-formation field, the first goal of this work was to obtain precise measurements of distances and proper motions of young stars in the Ophiuchus and the Serpens/Aquila regions by performing multi-epoch VLBI observations with the Very Long Baseline Array (VLBA). From our observation, we were able to further investigate the structure of the clouds, derive orbital parameters of binary systems and examine the relation between the properties of young stars, such as evolutionary stage and multiplicity, and their level of radio emission detectable on VLBI baselines.
The second part of the thesis focused on the source Sgr A*, which is associated with the nearest supermassive black hole, at the Galactic Center. High angular resolutions, only attainable with VLBI at millimeter wavelengths, are needed in order to detect the smallest scales and investigate phenomena related to black hole accretion and jet launching. We initiated operations for mm-VLBI observations at the Large Millimeter Telescope and performed a 3.5-mm VLBI experiment in concert with the VLBA. Because at this short wavelength the effect of the atmosphere on interferometric visibilities becomes severe, we developed and used non-imaging methods to study the millimeter emission from Sgr A*. We determined the intrinsic shape and orientation of the source at individual epochs, and interpreted the detection of substructure in the source image as possibly introduced by the interstellar medium in the direction of the Galactic Center.

I present evidence for the existence of a new young moving group (MG) in the Northern hemisphere -- the Pisces MG, based on optical spectroscopy and kinematic data from the Gaia TGAS catalog. Constituents of moving groups provide extremely useful tests of pre-main sequence evolution and are prime targets for direct imaging of exoplanets and circumstellar material. Whilst the majority of searches for nearby, young moving groups have focused on candidates in the Southern hemisphere, the Northern hemisphere remains relatively untapped. Motivated by the potential to find new young stars in the Northern hemisphere we compiled a list of several thousand short-period, X-ray active FGK stars (8 < V < 13) from the all-sky surveys of SuperWASP and ROSAT, respectively, and obtained follow-up optical spectroscopy for ~300 to acquire radial velocities and ages. Using Li abundance as the primary age-dating technique we identified a sub-set of young (5-200 Myr), likely-single stars and calculated their Galactic space velocities. From this young sample, we identified 15 which are co-moving, possibly co-eval and have unique space velocities: close to the Octans-Near group, but to no other previously identified MGs. This new grouping of stars would constitute the first nearby, young MG to be discovered solely in the Northern hemisphere. Given the large velocity distribution of these co-moving objects, we contemplate that these may be part of a larger structural complex, perhaps similar to that of the Local Association. In this talk I will discuss 1) how we generated our initial target sample of potentially-young objects; 2) how we measured spectroscopic parameters; 3) the impact TGAS data has made to our analyses; 4) the potential existence of the Pisces MG and 5) prospects for future searches of young, nearby stars.

Marzo

New multi-line mapping surveys of molecular clouds (e.g., CHaMP, ThrUMMS), are enabling an unprecedented demographic analysis of the physics of entire cloud populations. Key insights from such surveys include (but are not limited to): (1) The existence of a vast population of sub-thermally excited, massive dense clumps, the majority of which are not engaged in vigorous star formation; (2) The pressure-stabilisation of these clumps against dispersal by their overlying envelopes, implying long (several ×10^7 yr) cloud lifetimes; (3) A new CO → H2 conversion law accounting for these numerous pc-scale, low-excitation, high-opacity and high column density clumps, suggesting the total molecular mass of clouds, from pc to kpc scales in the Milky Way, may be underestimated by a factor of 2–3, and increasing the gas depletion timescale by the same factor; (4) A revision to the concept of large molecular clouds, including GMCs, to be structures composed of pc-scale clumps (∼75% by mass) connected by a more diffuse, large-scale envelope (∼25% by mass); and (5) Evidence for widespread flows of molecular material, both onto and away from existing cloud structures, on timescales consistent with the long cloud lifetimes and the overall low star formation efficiency in the Milky Way. We summarise these results and discuss implications for our understanding of star formation and the life cycle of molecular clouds.

In this talk I will give an overview over my latest results to compare current observations with latest 3D radiation MHD simulations of turbulent protoplanetary disks. I will focus on the dust thermal emission in protoplanetary disks, covering the outer regions which emit in the sub/mm and the inner regions which are expected to be thermally ionized and to emit in the near infrared.
In the first part of my talk I will discuss the recent works by Flock et al. 2015 and Ruge et al. 2016 which are able to explain ring formation and dust concentration at the dead-zone outer edge. In these works we show that ALMA is able to resolve these structure in the dust continuum emission. In the second part of my talk I will focus on the results of first 3D radiation non-ideal MHD simulations including the inner dust rim of protoplanetary disk (Flock et al. 2016a, Flock et al. 2016b). The results show the detailed shape of the inner rim and they compare well with observational constraints. Synthetic images of the thermal dust emission in the near infrared are presented and compared with recent interferometry observations. Finally I will draw conclusions on the results and discuss about the possibility to observe MRI activity with current telescope facilities.

Massive stars dominate the galactic environments and the full picture on how they form has not been obtained yet. In fact, this is a hot topic in the modern astronomy. In the last few years large surveys have apported new clues and have dramatically changed our view on massive star formation. These blind surveys allow to study ALL evolutionary stages of massive star formation in an unbiased way.
The GLObal view of STAR formation survey is an ambitious project that will observe the galactic plane by using interferometric VLBI, submm/FIR and VLA observations. In this talk I will focus on the Galactic plane VLA survey, where we observed simultaneously the continuum and, Methanol, Formaldehyde and Radio Recombination Lines. Also, I will talk about our recent results in the range l = 28degrees to 36degrees and the galactic center region.

Abril

Mayo

This talk presents new determinations of the stellar-to-halo mass relation (SHMR) at z = 0 − 10 that match the evolution of the galaxy stellar mass function, the SFR − M relation, and the cosmic star formation rate. We utilize a compilation of 40 observational studies, corrected for potential biases. Using our robust determinations of halo mass assembly from the several cosmological N-body simulations and the SHMR, we infer star formation histories, merger rates, and structural properties for average galaxies. Our main findings: (1) The halo mass M50(z) above which 50% of galaxies are quenched coincides with sSFR/sMAR~1, where sSFR is the specific star formation rate and sMAR is the specific halo mass accretion rate. (2) M50 increases with redshift, presumably due to cold streams being more efficient at high redshift while virial shocks and AGN feedback become more relevant at lower redshifts. (3) The ratio sSFR/sMAR has a peak value, which occurs around Mvir ≈ 2 × 10^11Msun . (4) The stellar mass density within 1 kpc, Σ1, is a good indicator of the galactic global sSFR. (5) Galaxies are statistically quenched after they reach a maximum in Σ1, consistent with theoretical expectations of the gas compaction model; this maximum depends on redshift. (6) In-situ star formation is responsible for most galactic stellar mass growth, especially for lower-mass galaxies. (7) Galaxies grow inside out. The marked change in the slope of the size–mass relation when galaxies became quenched, from d log Reff /d log M 0.35 to 2.5, could be the result of dry minor mergers

Ultra-Compact (UC)HII regions represent a very early stage of massive star formation whose structure and evolution are not yet fully understood. Interferometric observations in recent years show that some UCHII regions have associated compact sources of uncertain nature. Based on this, we started a high-resolution VLA observational campaign at several of selected UCHII regions in order to report additional cases of compact sources embedded in UCHII regions. As a preliminar result, we find 13 compact sources associated to 9 UCHII regions. Although unveiling the nature for the newly detected sources is a work in progress, we assess some of their observational properties. According to the results, we can distinguish between two classes of compact sources. One class corresponds to sources that probably are deeply embedded in the dense ionized gas of the UCHII region. These sources are being photo-evaporated by the exciting star of the region. They may play a crucial role in the evolution of the UCHII region as the photo-evaporated material could replenish for 10^4 − 10^5 yr the expanding plasma and might provide a solution to the so-called 'lifetime' problem for these regions. The other class of compact sources is not associated with the densest ionized gas of the region. Most of these sources appear unresolved and their properties are varied. We speculate on the similarity between these sources and those of the Orion population of radio sources.

The interstellar medium (ISM) plays an important role in the evolution of galaxies, and the best way to study it is by observing emission lines from the gas itself in the far infrared (FIR). With modern telescopes we are just starting to peak into the ISM of galaxies during the Epoch of Reionization (EoR), with very surprising results. My work is to invoke supercomputing powers to establish a better understanding of such observations. After a brief recap of the past few years in high-z FIR line observations, I will present the model SÍGAME; SImulator of GAlaxy Millimeter/submillimeter Emission, my main work here at the School of Earth and Space Exploration (SESE). SÍGAME builds on the output from cosmological hydrodynamic simulations of galaxy evolution to calculate the FIR line emission from different elements at any redshift desired. As examples of the method, recent results will be shown for [CII], [OI] and [OIII] of star-forming galaxies at z~6, forming part of a paper recently submitted. We find that [CII]-SFR and [OIII]-SFR power law relations come out naturally from the simulations, and I will compare with observations available at z > 5. By adopting different assumptions, we quantify how metallicity affects the [CII]-SFR relation and through a principle component analysis (PCA) we find that the the [CII] luminosity correlates most strongly with galaxy-averaged star formation rate surface density, but that molecular gas mass fraction and metallicity are also important. Finally, I will dive into future plans with SÍGAME.

We discuss the mechanism of cluster formation in a numerical simulation of a molecular cloud (MC) undergoing global hierarchical collapse, focusing on how the gas motions in the parent cloud control the assembly of the cluster. The global collapse implies that the star formation rate (SFR) increases over time. The collapse is hierarchical because it consists of small-scale collapses within larger scale ones. The small-scale collapses consist of clumps that are embedded in the filaments and falling on to the large-scale collapse centres. The stars formed in the early, small-scale collapses share the infall motion of their parent clumps, so that the filaments feed both gas and stars to the massive central clump. This process leads to the presence of a few older stars in a region where new protostars are forming, and also to a self-similar structure, in which each unit is composed of smaller scale subunits that approach each other and may merge. Because the older stars formed in the filaments share the infall motion of the gas on to the central clump, they tend to have larger velocities and to be distributed over larger areas than the younger stars formed in the central clump. Finally, massive stars only form once the local SFR is large enough to sample the IMF up to high masses. In combination with the increase of the SFR, this implies that massive stars tend to appear late in the evolution of the MC, and only in the central massive clumps. We discuss the correspondence of these features with observed properties of young stellar clusters, finding very good qualitative agreement.

Octubre

Comparing data on the kinematics of the Solar neighborhood from TGAS Gaia DR1 to newly constructed made-to-measure dynamical models of the Milky Way we propose a novel explanation for the Hercules stream consistent with recent measurements of the extent and pattern speed of the Galactic bar. The model matches the 3D density of the Red Clump Giant stars (RCGs) in the bulge and bar as well as stellar kinematics in the inner Galaxy, with a pattern speed of 39 km/s/kpc. Cross-matching this model with TGAS Gaia DR1 data combined with RAVE and LAMOST radial velocities, we find that the model naturally predicts a bimodality in the U-V-velocity distribution for nearby stars which is in good agreement with the Hercules stream. In the model, the Hercules stream is made of stars orbiting the Lagrange points of the bar which moves outwards from the bar's corotation radius to visit the Solar neighborhood. This new picture of the Hercules stream naturally predicts that the Hercules stream is more prominent inwards from the Sun and nearly absent only a few 100 pc outwards of the Sun, and plausibly explains that Hercules is prominent in old and metal-rich stars.

Studying the ionization sources, dynamics of the ionized gas and the interplay between it and other phases of the ISM and the stellar populations in local galaxies is essential to understand their formation and evolution.
Integral field spectroscpy (IFS) is a tool that lets us study ionized gas in local galaxies with unprecedented detail. I would like to share several projects that I am involved with that make use of IFS to study different aspects of the ionized gas: the relation between nitrogen abundance (N/O) and the stellar population content of star-forming galaxies from the CALIFA survey; the locality of the effect of close interactions in the star formation of CALIFA galaxies; the presence and significance of ionized gas in early-type galaxies from MUSE data; the interplay between AGN outflows and winds and the ISM of disk galaxies from CALIFA and MUSE data, and the effect of direct, face-on collissions in the star formation and dynamics of a sample of ring galaxies from Calar Alto / CALIFA and MUSE data. All these projects contribute to the understanding of the sources and dynamics of ionized gas and its role on the evolution of galaxies in the local universe.

The so--called jellyfish galaxies are objects exhibiting disturbed morphology, mostly in the form of tails of gas stripped from the main body of the galaxy. Several works have strongly suggested ram pressure stripping to be the mechanism driving this phenomenon. GAs Stripping Phenomena in galaxies (GASP) with MUSE is an ESO large program awarded 120 hours of time with the IFU MUSE to observe galaxies with evidences of gas stripping. I will present the goal and characteristics of the survey, and show some of the first results now that 80% of the targets have been observed.

Noviembre

Planetary nebulae (PNe) are one of the last phases in the evolution of low/intermediate mass stars (< 8 Msun), characterized by extended diffuse ionized and neutral gas surrounding the dying hot cores. Their immediate precursors are stars in the asymptotic giant branch (AGB), characterized by a strong mass-loss, followed by a short (100-10000 yr) transitional post-AGB phase. While the morphology of the mass-loss in the AGB phase is usually spherically symmetric, PNe show complex bipolar/multipolar structures. A few post-AGB stars, the water fountains (WFs), may represent the first manifestation of collimated mass-loss in evolved stars. These sources are characterized by collimated jets traced by high-velocity water masers. The study of WFs and very young PNe is crucial to understand the variety in the morphology shown by PNe. Through polarimetric observations of maser-emitting PNe and WFs is possible to have a detailed picture of the magnetic field (structure and strength) associated with these sources. Magnetic fields are a key ingredient in the early evolution and shaping process of PNe, as well as in the stellar mass-loss. Radio continuum observations provide information about emission processes (thermal/non-thermal) associated with WFs and PNe. In this talk, I will present our recent results on polarimetric observations toward maser-emitting PNe.

In this talk I will present results from our latest work in which we use a suite of high-resolution cosmological dwarf galaxy simulations to test the accuracy of commonly used mass estimators from Walker et al. (2009) and Wolf et al. (2010), both of which depend on the observed line-of-sight velocity dispersion and the 2D half-light radius of the galaxy, Re. The simulations are part of the Feedback in Realistic Environments (FIRE) project and include 12 systems with stellar masses spanning 10^5-10^7 M⊙ that have structural and kinematic properties similar to those of observed dispersion-supported dwarfs. Both estimators are found to be quite accurate: M_Wolf/M_true = 0.98^{+0.19}_{-0.12} and M_Walker/M_true =1.07^{+0.21}_{-0.15}, with errors reflecting the 68 per cent range over all simulations. The excellent performance of these estimators is remarkable given that they each assume spherical symmetry, a supposition that is broken in our simulated galaxies.

Diciembre

I will present the main results of our analysis of the local metallicity of the ionized gas for more than 9×10^5 star forming regions (spaxels) located in 1023 nearby galaxies included in the SDSS-IV MaNGA IFU survey. Among them, I will show the local mass - metallicity relation; its weak relation with global parameters as well as the lack of secondary relation of the global MZR with the SFR. We also explore the impact of the gas fraction in the local enrichment of MaNGA galaxies and comparisons with simple chemical evolutionary models. At kpc scales, the observed metallicity can be explained as a local version of the well-known gas regulated chemical model with outflows driven by stellar winds and SN explosions.

Enero

Many luminous Early Type Galaxies (ETGs; M_B < -20.5 mag) are characterized by depleted stellar cores, i.e. marked flattenings of the inner light distribution relative to the outer profile of the ETG spheroid.The structural characteristics of cores clearly depend on the formation history of the ETG, and in the last decades they have been shown to correlate with the mass of the central Super-Massive Black Hole (SMBH). This addresses to a link between the formation of the SMBH and that of the core.It has been suggested that Black Hole (BH) binaries, established during dry (i.e. gas-poor) mergers which shaped the ETG, kick stars out of the galaxian nucleus via three-body interaction, before coalescing into the central SMBH.In this talk, this "binary BH scouring scenario" is tested at its extremes by investigating the galaxies with the alleged largest cores found in the Local Universe; alternative core formation scenarios are promoted.

Cosmic acceleration is one of the most important issues to be explored by modern observational cosmology. Cosmic acceleration can be explained by either modifying General Relativity on cosmological scales, or within the framework of the standard cosmological model this implies that ~70 per cent of the Universe is dominated by a new component called “dark energy” with the unusual physical property that opposes the attractive force of gravity. I will present the results of the Baryon Oscillation spectroscopic Survey (BOSS) that uses the baryon Acoustic Oscillation to extract information about the equation of state of dark energy. The BAO feature corresponds to the maximum distance travelled by acoustic waves in the matter-radiation fluid during the period from matter/radiation equality to their decoupling at z~1100 and then stretched by expansion of universe. This feature can be seen as a standard ruler allowing us to study the history of the expansion of the Universe and infer cosmological information. I will present the latest cosmological constraints in dark energy and extensions of LCDM that we can extract combining BAO with the cosmic microwave background (CMB) data and Type Ia supernova (SN) data.

Hypercompact HII regions are ionized gas regions associated with the earliest stages of high-mass star formation. These regions are characterized by their small sizes (􏰁smaller than 0.05 pc), high electron densities (larger than 1e6 cm^−3) and emission measures exceeding 1e9 pc/cm^6. Unlike ultracompact HII regions, which typically host a cluster of massive stars, hypercompact (HC) HII regions are thought to surround a single star or perhaps a binary system. As such, HC HII regions present us with a laboratory to study the physical processes involved in the formation of single stars, without the complicating phenomena of a cluster environment.In this work, we study five candidate HC HII regions originally observed at 1.3 and 3.6 cm. These regions were selected because they show 6.7 GHz methanol maser emission ( a tracer of high mass star formation) but they show little or no emission at 6 and 20 cm (indicating a pre-ultracompact HII region stage). All sources show extended 8 and 24 micron emission further supporting their identification as very young high-mass star-forming regions.To confirm the classification and to understand better the nature of these regions, we made observations at 2 and 6 cm, using the Jansky Very Large Array (JVLA) with an angular resolution of about 2 arcsec. Here we report our detections, showing the radio images and the measured parameters.We present a preliminary analysis of our results, including the modeling of the spectra as uniform and non-uniform spheres.

Febrero

We present our study on the evolution of galaxy properties in compact groups over the past 3 Gyr. We are using the largest multi-wavelength sample to-date, comprised of 1770 groups (containing 7417 galaxies), in the redshift range of 0.01<z<0.23. To derive the physical properties of the galaxies we rely on ultraviolet (UV)-to-infrared spectral energy distribution modeling, using CIGALE. We find a significant increase of the number of the AGN-hosting galaxies as we are moving towards lower redshifts, and we report the absence of Seyfert 1 nuclei. We also show that at any given stellar mass, galaxies in dynamically old groups are more likely to host an AGN. Our results also suggest that during the 3 Gyr period covered by our sample, the star formation activity of galaxies in our groups has been substantially reduced (3-10 times). Moreover, their observed UV-optical and mid-infrared colours are consistent with star formation rate histories, which are significantly different from those of galaxies in the field and in clusters, as the former spend more time tran- sitioning through the green valley. We also find evidence that the morphological transformation of late-type galaxies into earlier types, occurs during the mid-infrared green valley transition rather than during the UV-optical one. Examining the emission line ratios and gas velocity dispersions of the late-type galaxies located below the star forming main sequence, we find evidence of shocks.

Stellar masses of galaxies are frequently obtained via SPS fitting to observed photometry, or galaxy spectra. "State of the art" methods resolve spatial structures within a galaxy to asses the total stellar mass content. In comparison to unresolved studies, resolved methods yield higher fractions of stellar mass for galaxies. In this talk we will demonstrate that current methods commonly deliver biased resolved spatial structures. We will discuss the cause of this bias, an introduce a new method, based on Bayesian statistics, aimed to mitigate the bias. We applied this method to M51, and a pilot sample of spiral galaxies. We will compare quantitatively the application of both methods and discuss the results.

Marzo

We summarize our comprehensive gas surveys of some of the most luminous (Lbol 1e5 to 1e7 Lsun), deeply embedded (optically obscured) star formation regions in the Milky Way, which are the local cases of massive star clusters and/or associations in the making. Our approach emphasizes multi-scale, multi-resolution imaging in dust and free-free continuum, as well as in molecular- and hydrogen recombination lines, to trace the multiple gas components from < 0.1 pc (core scale) all the way up to the scales of the entire giant molecular cloud (GMC), or ~ 100 pc. We highlight our results on W49A, the most luminous Galactic star formation region (Lbol ~ 2e7 Lsun), which appears to be forming a young star cluster (or a binary star cluster) with M_star ~ 1e5 Msun that may remain bound after gas dispersal. We also highlight our recent result on the G33.92 region (Lbol ~ 3e5 Lsun), where ALMA mapping reveals that the cluster-forming accretion flow is arranged in a fragmented spiral-like structure from clump to core scales. Preliminary results in a handful of other regions will be shown.

We have performed a selection of intermediate mass stars (spectral types F5 or earlier) candidates that potentially exhibit protoplanetary disks based on infrared data from the 2MASS and WISE catalogs. Of particular interest are Herbig Ae/Be stars, which exhibit near infrared excesses produced in the inner wall located at the dust destruction radius and emission lines produced by accretion mechanisms. The area surveyed is ~1000 square degrees and includes the Orion OB stellar associations. Distances normally assumed for young stars located in this region range from 300 pc to 500 pc. We have initiated optical spectroscopic follow-up observations of selected candidates using the spectrographs OSU-CCDS at the observatory MDM and the Boller & Chivens at the observatory San Pedro Martir. Our main goal is to build a large scale census of protoplanetary disks around intermediate mass stars that will contribute to a better understanding of the star forming and disk evolution processes, as well as possible relationships between the environment and the spatial distribution of stars in this mass regime.

Galaxies like our Milky Way can be described in terms of their
structure, dynamics, and stellar populations. Some very robust
correlations between galaxy structural properties, such as total
luminosity, maximum circular velocity, and size show rather small
scatter, hinting at well-regulated galaxy formation processes.
A major challenge to understanding these scaling relations, and
ultimately galaxy formation and evolution, is the elusive interplay
between visible and dark matter. I will discuss the latest
constraints to galaxy scaling relations and their link with
modern cosmological models.

All massive galaxies harbor a supermassive black hole in their centers. A phase during which the central black hole accretes the surrounding matter and grows considerably is referred to as the Active Galactic Nucleus (AGN). The strong radiation from the gas spiraling into a black hole is partially reprocessed by the dust clouds placed further out in a roughly toroidal shape ("the dusty torus") and is released in the infrared. Thus, the ratio of the AGN and torus luminosities (L_AGN/L_tor) is commonly used as the dust covering factor (CF) proxy. Using state-of-the-art Monte Carlo radiative transfer code, we critically investigated the relation between the L_AGN/L_tor and the CF. We found that in most of the cases L_AGN/L_tor significantly over- or underestimates the true CF. Our results provide a new straightforward way to account for the effects leading to this and obtain true CFs. We demonstrate the importance of these results for inferring the obscured fraction of AGNs as a function of L_AGN by applying the corrections to the two large samples from the literature, showing that CF has much weaker dependence on L_AGN than previously thought. Our results suggest a higher fraction of obscured AGNs at high luminosities than those found by X-ray surveys, partially due to the presence of a Compton-thick AGN population, which is missed by X-ray surveys, but not by infrared.

One of the most exciting and unsolved problems in Astrophysics is figuring out the origin of the Ultra High Energy Cosmic Rays. These are particles having an energy of about 100 EeV (which is a billion times the energy of the Higgs boson) and arrive on the Earth from outside the Galaxy, but their origin remains unknown. It has been suggested that relativistic shocks in extragalactic sources like Active Galactic Nuclei may accelerate the highest energy cosmic rays. The maximum energy to which cosmic rays can be accelerated depends on the structure of magnetic turbulence near the shock but recent theoretical advances indicate that relativistic shocks are probably unable to accelerate particles to energies much larger than 1 PeV. We study the hotspots of powerful radiogalaxies, where electrons accelerated at the termination shock emit synchrotron radiation. The cut-off of the synchrotron spectrum is typically observed between
infrared and optical frequencies, indicating that the maximum energy of non-thermal electrons accelerated at the shock is about 1 TeV for a canonical magnetic field of 100 micro Gauss. Based on theoretical considerations we show that this maximum energy cannot be constrained by synchrotron losses as usually assumed, unless the jet density is unreasonable large. We test this result by considering a sample of hotspots observed with high spatial resolution at radio, infrared and optical wavelengths.

Despite many decades of theoretical effort and large volumes of high-precisionobservations, obtaining ages for stars accurate to within ~10% remains a difficult and often elusive challenge for stellar astrophysics. In constrast, cosmologists can claim a precision of 1% for the age of the Universe! In this talk I provide a general overview of the various techniques at our disposal to estimate the ages of young, nearby stars. I will adopt a hierarchial approach in this review, in order of decreasing precision and/or utility. Firstly I will examine "semi-fundamental" techniques that rely on well-understood physics - the lithium depletion boundary method and kinematic tracebacks. Next I will discuss the "model-dependent" methods that are subject to various inputs in the stellar physics - the isochronal method, upper main-sequence fitting and asteroseismology. Finally I will describe the "empirical" methods, which rely on, at their very least, a non-monotonic age-functional form that is often poorly constrained - rotation, activity and lithium in FGK stars. In my summary I provide a forecast for future stellar chronometry, focusing on the prospects expected from the GAIA mission which should provide micro-arcsecond precision astrometry (due for first data release in Summer 2016).

The Gaia mission will provide us with an unprecedented stereoscopic map of the heavens and will likely be the astronomical data resource for decades thereafter, representing a tremendous discovery potential. It will measure parallaxes and proper motions for every object in the sky brighter than magnitude 20 - amounting to 1 billion stars, galaxies, quasars and solar system objects. I will summarise the Gaia mission, performance so far and some early discoveries. The complexities of the final Gaia catalogue, and the science we want to extract from it, will force us to be very ambitious in the way we publish the Gaia catalogue. In order to unlock the full potential, we need to integrate the Gaia catalogue with other sky surveys and provide advanced statistical approaches and visualisation tools to allow the community to explore the data, do the science they expect and to facilitate the discovery of the unexpected. I will mention some of the efforts that are being undertaken within the scientific community to tackle these aspects and how these along with the Gaia data will be made available.

Junio

Ring nebulae are interstellar bubbles of ionized gas that have swept-up the surrounding interstellar medium after the mass loss episodes experienced by their massive progenitors, especially during the Wolf-Rayet phase. The presence of stellar ejecta in ring nebulae allows us to better understand the nucleosynthesis of massive stars and the effects of the H-burning reactions on the elements involved in the CNO cycle. A detailed analysis of the chemical composition and abundance ratios of these elements provides us valuable information to constrain stellar evolution models of massive stars and the evolutive scenario of the stellar progenitors. Within this framework, we will present results from new spectroscopic data in the optical range of the Galactic ring nebulae NGC6888, G2.4+1.4, RCW58 and NGC7635 based on very deep observations obtained with the 10m GTC telescope and the 6.5m Clay telescope. In comparison with previous studies, these new observations have allowed us to derive physical conditions and chemical abundances with great accuracy in different zones of the nebulae. Therefore, we have been able to detect and localize areas of shocked gas, and investigate the presence of chemical inhomogeneities in these objects. Additionally, we will present the first determinations of C abundances in these ring nebulae based on the faint recombination line CII 4267 A as well as their implications when comparing with the predictions of stellar evolution models. These crucial results represent the first constrains on C abundances, providing long-awaited information on the action of the CNO cycle that controls the nucleosynthesis processes in massive stars.

Spectroscopy, as a tool, has permitted some of the most fundamental discoveries in the study of the Milky Way. With the growing number of Galactic surveys (e.g. the Gaia-ESO survey, GALAH, APOGEE) in medium and high resolution, the number of stars observed will amount to several hundred thousands in the near future requiring precise analyses of their spectra in terms of their atmospheric parameters and chemical abundances.
In this talk, I will present the main spectroscopic methods for the derivation of the stellar atmospheric parameters (namely the effective temperature, surface gravity, metallicity) and the fields where stellar characterization plays a key role. In particular, these tools enable us to distinguish and define the different stellar populations our Galaxy is composed of. I will also describe why this work comes in good time for the analysis of the Gaia data, a very anticipated mission for the study of our Galaxy.

For decades we have understood the star clusters as a bound association of stars that share their age and their metallicity. This was due to the understading that stars inside a star clusters formed from the same mother cloud. However, during the past ~10 years new observations have been challenging this idea. Multiple stellar populations have been observed inside particular star clusters, where stars with different metallicities have formed in large numbers inside clusters. In this seminar, I will present the background of this open problem in the field and the possible solutions to this problem.

Agosto

During the last 30 years spectral studies of the broad iron K-alpha line and the Compton hump in the X-ray spectra of AGN have shown that the X-ray source illuminates the innermost part of the accretion disc in these systems. Further support to this hypothesis is provided by the detection of delays between the X-ray continuum variations and the spectral features that are supposed to be produced by X-ray reflection (mainly the soft-excess and the iron line). The X-ray reprocessing by the disc should also affect the X-ray continuum variability properties. The observed X-ray power-spectra should show a prominent dip at high frequencies and an oscillatory behaviour, with a decreasing amplitude, at higher frequencies. These reverberation “echo” features should be
more prominent in energy bands where the reflection component is more pronounce, and should depend mainly on the central black hole mass and the X-ray source height. The detection of the X–ray reverberation signals in the PSDs can provide further evidence for X-ray illumination of the inner disc in AGN and can be used to map out the geometry of the inner accretion flow (which cannot be studied in any other way).

I will present forecasts on galaxy cluster counts from the X-ray survey with the future eROSITA mission. Clusters of galaxies are the largest gravitationally-bound objects in the Universe. Thereby clusters are ideal tracers of cosmic expansion and structure formation that allow tight constraints on the average cosmic density of matter and of other fundamental cosmological parameters. In this talk I will show how we study the detection efficiency of galaxy clusters of the upcoming eROSITA X-ray mission. The cluster detection probability is investigated by means of extensive and dedicated Monte Carlo simulations, and employing a state-of-the-art source detection technique we determine a cluster detection eefficiency based on the cluster fluxes and sizes. Using this eROSITA cluster selection function, we found that eROSITA will be able to detect a total of 1.36x10^5 clusters in the whole sky. This cluster number will allow eROSITA to put stringent constraints on the dark matter and dark energy models.

Potentially habitable planets within the habitable zone of M-dwarfs are affected by tidal interaction. We studied the tidal evolution in GJ 667C using a numerical code we call TIDEV. We reviewed the problem of the dynamical evolution focusing on the effects that a rheological treatment, different compositions and the inclusion of orbital perturbations, have on the spin-down time and the probability to be trapped in a low spin-orbit resonance. Composition have a noticiable effect on the spin-down time, changing, in some cases, by almost a factor of 2 with respect to the value estimated for a reference Earth-like model. We calculated the time to reach a low resonance value (3:2) for the configuration of 6 planets. Capture probabilities are affected when assuming different compositions and eccentricities variations. We chose planets b and c to evaluate the probabilities of capture in resonances below 5:2 for two compositions: Earth-like and Waterworld planets. We found that perturbations, although having a secular effect on eccentricities, have a low impact on capture probabilities and nothing on spin-down times. The implications of the eccentricity variations and actual habitability of the GJ 667C system are discussed.

Septiembre

During the last decade, the use of optical/infrared interferometry has grown up to study stellar physics. Facilities like the Very Large Telescope Interferometer (VLTI) in Europe, or the CHARA array in the United States have proven to play a key role to perform high-angular resolution observations. The scientific cases addressed with this technique go from the study of (massive) young stellar objects to multiple systems or evolved stars. In this talk, I will perform a review of the basic principles of the optical/near-infrared interferometry and of the current European facilities to use this observational technique. Particularly, I will describe the main differences between radio and infrared interferometry (e.g., the observables and the problem of image reconstruction). I will provide a review of the current (and future) instruments available at the ESO VLTI, enhancing their advantages and limitations. Finally, as a show case, I will present my current studies of massive stars using this technique, paying special attention to the characterisation of multiple systems and of the winds of the massive stars at the Galactic Center.

We test the predictions of spectral synthesis models based on seven different massive-star prescriptions against Legacy ExtraGalactic UV Survey (LEGUS) observations of eight young massive clusters in two local galaxies, NGC 1566 and NGC 5253, chosen because predictions of all seven models are available at the published galactic metallicities. The high angular resolution, extensive cluster inventory, and full near-ultraviolet to near-infrared photometric coverage make the LEGUS data set excellent for this study. We account for both stellar and nebular emission in the models and try two different prescriptions for attenuation by dust. From Bayesian fits of model libraries to the observations, we find remarkably low dispersion in the median E(B - V) (~0.03 mag), stellar masses (~10^4 M⊙), and ages (~1 Myr) derived for individual clusters using different models, although maximum discrepancies in these quantities can reach 0.09 mag and factors of 2.8 and 2.5, respectively. This is for ranges in median properties of 0.05-0.54 mag, 1.8-10 × 10^4 M⊙, and 1.6-40 Myr spanned by the clusters in our sample. In terms of best fit, the observations are slightly better reproduced by models with interacting binaries and least well reproduced by models with single rotating stars. Our study provides a first quantitative estimate of the accuracies and uncertainties of the most recent spectral synthesis models of young stellar populations, demonstrates the good progress of models in fitting high-quality observations, and highlights the needs for a larger cluster sample and more extensive tests of the model parameter space.

I review the evolution of our understanding on the nature, structure and dynamics of molecular clouds (MCs). I start with the first observations of molecular and the quick realization that they imply supersonic motions in MCs, which initially were interpreted as gravitational collapse. However, it was soon argued that global collapse of the clouds would imply a SFR larger than observed by two orders of magnitude. Then it was proposed that MCs were supported against collapse by some agent causing them to survive for much longer times than their free-fall times. I then review the two main paradigms of cloud support: magnetic and turbulent, discussing their basic features, and the reasons leading to their demise. Finally, I discuss the evidence that in the last half-decade has suggested a return to the global collapse scenario, and how the SFR is regulated in this case.

Born-again planetary nebulae (PNe) represent unique objects in the evolution of thecircumstellar medium around low-mass stars (M < 8 Msun). The central starsof these PNe are thought to have experienced a very late thermal pulse when they were in the white dwarf track that produced the ejection of newly processed material inside the old PN. This scenario offers the opportunity to study the wind-wind interaction and production and destruction of molecules and dust in human scales (~20-100 yr). In this talk I present a review of our multi-wavelength campaign to characterise bona-fide born-again PNe using ground-based telescopes and satellites.

Octubre

Despite much effort has been devoted to characterize the dusty tori in active galactic nuclei (AGN), very little is still known in those with high bolometric luminosity, mostly quasi-stellar objects (QSOs). This is mainly due to their compactness and sparseness in the local Universe. Mid-IR high angular resolution observations offer a good oportunity to step foward in their understainding. In this talk, I going to present new high angular resolution mid-IR data (0.3 arcsec) obtained with the IR camera CanariCam (CC) on the 10.4m Gran Telescopio CANARIAS, for a sample of 20 nearby QSOs. The analysis of the images at Si2 band (8.7 um) reveals that the mid-IR emission is unresolved in the majority of QSO at scales < 600 pc. We compare the IRS/Spitzer and the ground-based CC spectra and find that the spectral shapes are similar, and hence adopt the former to isolate the AGN component. We find that on average the AGN contributes 85 per cent of the total mid-IR emission within the IRS/Spitzer apertures (~3.5 arcsec), while the rest can be atribbuted to starburst emission. We use unresolved near-IR emission from the literature and the starburst-subtracted mid-IR spectra to constrain the physical and geometrical parameters of clumpy dusty torus models of Nenkova et al. We find that for most QSOs the unresolved SED and spectroscopy can be well reproduced by the models without the inclussion of a hot dust component, as propose in the literature. Finally, a statistical comparison between the parameters of the dusty torus of QSOs derived by us and the dusty torus of some Seyfert 1s and 2s studied with a similar technique for others authors, shows that the properties of the dusty torus in QSOs are intrinsically different from those of Seyfert 1 and 2 nuclei. Nevertheles, in QSOs the parameters derived (e.g., the covering factor) are consistent with the optical classification of QSOs as type 1 AGN. An analysis on the dependence of the covering with the bolometric luminosity suggests that these differences can be attributed to dusty structures that have been partly evaporated and piled up by the higher intensity radiation field in QSOs, as proposed by a receding torus scenario.

The relevance of galaxy bulges as central pieces in the study of galaxy formation is nowadays well settled. Bulges come in two flavours: classical and disk-like bulges. Different formation mechanisms have been proposed to explain this dichotomy and therefore understanding their demography is of vital importance to unveil galaxy formation. In this talk, I will present the results of a careful photometric analysis of the galaxies present in the CALIFA survey. Using the available SDSS photometry, we found a zoo of morphological structures (single and double bars, broken exponential profiles, etc), with bulges following this diversity in terms of a wide range of masses and concentrations (i.e., Sersic index). In particular, I will focus on the observed properties of bulges in lenticular galaxies where, by definition, they are suppose to play an important role in their evolution. Combining the photometric analysis of the galaxy bulges with the stellar kinematic information about their rotational support (angular momentum), we suggest that lenticular bulges were mainly formed through dissipational processes at high redshift, either wet major mergers or coalesce of giant star-forming clumps. I will discuss these results in the general context of lenticular galaxies formation.

Noviembre

We are at present in an very exciting era for the study of how planets form. During the previous decades, observations with powerful radiointerferometers, specially the Very Large Array (VLA), have well established that planet formation is a natural consequence of the star formation process itself. Planets are most probably formed as dust evolve in the circumstellar disks around Young Stellar Objects (YSOs). It is now that, the extraordinary observing capabilities of the Atacama Large Millimeter Array (ALMA) are offering us an unprecedent level of detail of circumstellar disks around YSOs. The recent ALMA observations with very high angular resolutions of several disks are revealing several structures, consequences of the dust evolution, and most probably associated with the initial stages and/or ongoing planet formation. However, the contribution of the VLA to this field has not yet finished. Instead, the VLA with its recent upgrade, is still in the race and it is indeed revealing itself as a fundamental instrument to investigate the planet formation process. It seems necessary to still observe at longer millimeter wavelengths than ALMA in order to be able to penetrate very dense regions in the disks. This is specially critical at the earliest stages and at the innermost parts of the disks where, for example, terrestrial planets are expected to form. Here, I will present some very recent observations with the VLA of two very young circumstellar disks (HL Tau and HD 169142). I will also discuss how the combination of VLA and ALMA images is what actually could provide a giant step in the understanding of the planet formation process.

In this talk, I will show the recent results obtained in deep ALMA observations of the explosive outflow located in the heart of the Orion Nebula, the Orion Kleinmann-Low Nebula (Orion KL). These observations revealed over a hundred arcsecond wide and tens of arcseconds long high-velocity 12CO (J=2−1) streamers that approximately point to a central region where a young stellar massive system disintegrated very recently. The kinematics and morphology of the molecular streamers confirmed the explosive nature of the outflow in Orion KL. The energetics of the explosive outflow require the formation of a binary with an AU-scale or smaller semi-major axis. This event may have led to stellar merger which powered the explosion in the gas. Finally, I will show the latest efforts to reveal more cases where possible mergers events could led explosive outflows like the one in Orion KL.

I present an observational study of a sample of radio AGN sources. I study their radio polarization properties in a wide frequency range by observing with the 100-m Effelsberg telescope and the Very Large Array (VLA) interferometer. The aim was 1) to define a sample of candidates to contain an extreme environment around the SMBH and, 2) to study their environment by modeling of the polarization properties within a wide frequency range.
I select sources with no detectable flux polarization at 1.4GHz in the NVSS survey, characteristic of strong depolarization due to a high value of Rotation Measure (RM) and thus, of an extreme medium in these sources.
I performed single dish observations at 10.45 GHz using the 100-m Effelsberg telescope. At this high frequency, I detected polarized flux density on 30 sources, which became our high-RM candidates. Single dish follow-up in the 2 to 15 GHz frequency range, were performed to characterize their radio spectra and to determine their RMs. The polarization angle behavior deviates significantly from the lambda^2 law, suggesting that several Faraday screens are present in the intervening medium. I studied the most interesting high-RM cases through wide-band high sensitive observations at C and X bands using the JVLA. I modeled the polarization properties constructing a set of models which are combinations of simple internal and the external Faraday screens. This new approach of polarization study allows to spectrally resolve multiple polarized components of unresolved AGN with the result to trace some clumpy and dense region surrounding them. This new spectropolarimetry approach can be adopted as a new way to trace clumpy and dense regions surrounding the AGN.
Moreover, I will present a new project I am involved in which this new spectropolarimetry study is applied to a very specific class of objects: the Compact Symmetric Objects (CSOs), the nature of which is still matter of debate. Indeed, whether they are young radio sources (youth scenario) or compact radio sources embedded in a very dense medium (the frustrated scenario), is not clear yet.
The Stokes Q and U modeling will help to understand which of the two scenario is the most probable.
I will explain the “engulfed cloud model”, proposed by Begelman 1999 which is in favor of the youth scenario and that it could be tested with this new spectropolarimetry approach.

Febrero

I am presenting the results from the "Herschel Exploitation of the Local Galaxy Andromeda" (HELGA), a survey who observed our neighbour galaxy M31 in five IR bands. Taking advantage of Herschel sensitivity and spatial resolution, we address various issues related to the dust distribution and properties in Andromeda, and its relation to the spatial distribution and characteristics of the gas and stellar components. Dust in M31 extends well beyond its optical radius, and is gathered in well-defined recurrent patterns. Contrary to what is found in other galaxies, dust reaches the highest temperatures in the bulge, heated by the old stellar populations, and its (chemical) properties change radially. Using a panchromatic dataset we adopt physically consisted panchromatic model to fit the broad-band SED of each pixel in our data, to address the origin of dust scaling relations, at the spatial level of giant molecular clouds.

Marzo

Traditionally its been considered that turbulence in molecular clouds provides support against self-gravity. In order to do so, turbulence should be random, microscopic and isotropic. However, it is highly uncertain which sources of energy may provide such kind of turbulence, since it is highly dissipative, and most of the energy is involved at the largest scales, which furthermore, imply that it cannot be isotropic. In the present contribution we will discuss a set of observational and theoretical results, namely, the column density PDF, scaling relations, fragmentation of clouds into clumps and clumps into cores, formation and evolution of clouds and cores, Virial type relations, etc., which strongly suggest that nonthermal motions within molecular clouds, rather than kinetic energy providing support against collapse, might be very well the result of hierarchical and chaotic collapse

Some young open clusters and giant molecular clouds have been detected as gamma-ray sources in recent years. The level of gamma radiation suggests the existence of local injectors of cosmic rays in these objects. I will discuss the contribution of massive runaway stars and other supersonic objects to the cosmic ray population in young clusters and the origin of the observed gamma-ray emission.

We model the vertical structure of magnetized accretion disks subject to viscous and resistive heating, irradiation by the central star and magnetic pressure. We apply our formalism to the radial structure of magnetized accretion disks threaded by a poloidal magnetic field developed by Shu and coworkers. We consider disks around low mass protostars, FU Ori and T Tauri stars. We tested our formalism using different mass-to-Magnetic flux ratios and I will show how this essential parameter can strongly modify the disks structure.

We present the results of our mutlifrequency observations with the GMRT and the VLA of five large radio galaxies. These observations were made with the objectives of estimating their spectral ages and examining any evidences of diffuse extended emission at low radio frequencies due to an earlier cycle of

activity. While no evidence of extended emission due to an earlier cycle of activity has been found, the spectral ages have been estimated to be > 15 Myr for the oldest relativistic plasma seen in the regions close to the cores in these large sources. The spectra in the vicinity of the hotspots are somewhat steeper than theoretical expectations.

Mayo

Our view of the structure and dynamics of our Galaxy has progressed, pushed by the acquisition of ever larger datasets that encompass wider perspectives. At the dawn of the Gaia era, we are about to enter a phase of unprecedented detail in our view of our Galaxy. This opens up the possibility of using new analysis tools, or the use of traditional tools at newer scales. However, to extract the most of the Gaia database, it is necessary to immerse our theoretical models within Gaia mock catalogues to derive proper inferences about the structure of our Galaxy. In this talk we will review several tools developed by our group to construct and analyze realistic Gaia mock catalogues and some of the lessons we have learnt from them. In particular, we will present applications to the problems of characterizing the central bar of our Galaxy, the warp in the Galactic disk and identifying substructure in the stellar halo.

The Orion Nebula Cluster (ONC) is hosting a zoo of radio sources that has been known for decades. Additionally, the X-ray properties of its substantial YSO population have been studied in detail in the Chandra Orion Ultradeep Survey. With the advent of the newly expanded NRAO Very Large Array, we have returned to the ONC with deep simultaneous radio and X-ray observations using the VLA and Chandra. With this massive dataset, we have begun to obtain a deep census of radio sources in this region, including information on polarization and spectral indices, to systematically study YSO radio variability on time scales shorter than an hour, and to put this into the context of X-ray light curves and other source properties. Additionally, we have assembled a wealth of infrared data to assist the interpretation, including a new deep near-infrared survey (VISION) and Spitzer mid-infrared variability data obtained as part of the YSOVAR program. After presenting first results of the radio-X-ray program, I will finally discuss the prospects for radio-X-ray-IR variability studies of YSOs.

Junio

The key project “Chemical HErschel Surveys of Star form- ing regions” (CHESS), takes full advantage of the new opportunity offered by Herschel/HIFI and explores in a systematic way the frequency range between 480 and 1902 GHz in several star-forming regions. The goal of the project is to provide the first ever spectral census of this frequency range in a selected sample of sources covering the principal parameters and aspects of the star-formation process: mass of the forming star, its evolutionary status, and the interaction with the surroundings. In this talk I will focus on the results of the interstellar shock L1157-B1, in particular the studies of molecular species such as CO, H2O, CS, N2H+, among others.

Agosto

The new generation of sub-arcsecond resolution infrared (IR) polarimetric instruments, CanariCam on the 10.4-m Gran Telescopio CANARIAS (GTC) and MMT-Pol on the 6.5-m MMT, have opened a new window to reveal the cores of active galactic nuclei (AGN). Using both instruments, we have been able to 1) discover a highly polarized synchrotron core in Cygnus A, 2) study the torus of NGC 1068 as a hydromagnetical outflow wind, and 3) investigate the interaction of the jet with the ionization cones in NGC 1068. This talk will introduce the polarimetric modes of CanariCam and MMT-Pol, what can be learnt from polarimetric techniques observations, and the latest results on the study of AGN using IR polarimetric techniques.

Establishing an evolutionary sequence for high-mass young stellar objects is one of the hot topics of current star formation. Differently to the low-mass star formation case, high-mass stars reach the zero-age main sequence while they still undergo heavy accretion, and their powerful radiation pressure should halt the infall of material, thus inhibiting growth of the stellar mass beyond 8 Msun. Recent theories, however, propose that high accretion rates and/or accretion through massive disks could overcome this problem, and explain the formation of stars with masses up to 140 Msun. In this talk I will characterize, from an observational point of view, an evolutionary scheme for the massive star formation process: which starts with dense cores with almost no (star-formation) activity, and ends with the development of HII regions that disrupt their natal cloud. I will present recent results on the physical properties of dense cores, molecular outflows, circumstellar disks, and HII regions obtained with a number of different instruments including the Atacama Large Millimeter Array.

The effective supply and retention of gas in shallow gravitational potentials is a problem with implications in a diverse set of astrophysical systems. In particular, the magnitude of gas flows into mature dwarf galaxies can have large impacts on the star formation histories in these systems. In this talk, computational techniques will be used to show how such such weakly bound gravitational structures might be able to accumulate gas effectively. The implications for star formation in dwarf galaxies after their incorporation into a larger host halo will be presented.

Septiembre

The particular astrophysical site where r-process nuclei are synthesized remains open to more than one interpretation, being both type II supernovae and neutron-star binary mergers two likely astrophysical sites. These two mechanisms synthesized different quantities of r-process material and these differences should give rise to clear signatures in the enrichment pattern of r-process elements in galaxies and may ultimately help to constrain the dominant production mechanism. In this talk, a comparison between the propagation of the material ejected from both events will be presented. The enrichment of r-process material from these two mechanisms is analyzed in order to investigate the distribution of these nuclei along the galaxy.

Octubre

The recent decades have witnessed major advances in our understanding of the formation of solar-mass stars. However, the formation mechanisms of stars at the extremes of the mass range, that is, on one hand very massive stars and on the other brown dwarfs, remain poorly understood. I will summarize the main observational results presented in a meeting on massive star formation that took place in Puerto Varas, Chile and discuss some new observational perspectives for the future.

The evolution of the circumstellar envelopes of AGB and post-AGB is yet poorly understood. In particular, the mechanism(s) responsible for shaping the axisymmetric circumstellar envelopes observed towards bipolar Planetary Nebula sources remain unknown. The study of the collimated, high-velocity outflows observed towards post-AGB sources known as Water Fountain nebulae, could provide important clues about the nature of the engine shaping their circumstellar envelopes. In this colloquium I will present new results from ATCA and JVLA observations towards two representative members of the still small group of (16 confirmed up to date) Water Fountain sources.

Noviembre

During the last decades protostellar jets have been intensively studied at radio wavelengths. It is now well established that young stellar objects (YSOs) in their earliest stages emit radio emission at cm wavelengths which is associated with free-free emission from the base protostellar jets. Since these objects are deeply embedded in large amounts of dust and gas surrounding the protostar, radio observations have revealed as the best way to study the phenomena that takes place very near the protostar. We have now been able to study the environment of these protostars up to physical scales of only a few AU. However, as we have performed higher sensitive and higher angular resolution observations, we have also been able to discover new phenomena which, not only, have important implications for the star formation theory, but also add new interesting questions. Here, I will talk about two important results we have obtained in two star-forming regions. The first one, the discovery of synchrotron emission from a protostellar jet, imply that protostellar jets are able to accelerate particles up to relativistic velocities, even when these objects are considered the least powerful between astrophysical jets (AGN jets, micro quasars, etc..). Moreover, the detection of linearly polarized emission allows to study the magnetic field, one of the most important ingredients in the jet formation and collimation, but yet, one of the most unknown parameters in star formation. The second results is the observation, in real time, of the collimation of a protostellar wind, posing interesting questions on how jets are collimated in these systems.

The understanding of the Lyman alpha emission (Hydrogen n:2->1) in starburst galaxies needs multi-wavelength analysis of nearby sources with high-spatial resolution. The international project Lyman Alpha Reference Sample (LARS) was defined to carry out such task. In this talk I will describe the intriguing nature of Lyman alpha emission, and the observational limitations we face. The core of the talk will be the review of the most important results obtained by LARS so far, which have led to confirm that Lyman alpha escape is a multiparametric problem.

This colloquium will focus on water fountains, huge stars with collimated and high-velocity outflows, moments before their deaths as white dwarfs enveloped in beautiful planetary nebulae. I am going to present recent astrometric results from the fastest and farthest water fountain, and through that we will discuss 1, how VLBI astrometry using maser emission helps us to study water fountains 2, the morphology of water fountain outflows 3, the variability of water maser emission and 4, how all of these tell us something about the evolutionary link between AGBs and PNe.

I will start with a brief description of the GTC, the 10.4m telescope that Mexico has access to it. The I will discuss the projects that we are undertaking using GTC data. In particular, the search for high-z Lyman α sources in the SHARDS survey. Finally I will talk about another project which aim is the study of Lymanα sources at the epoch in which re-ionization was being completed. I will show the discovery of an overdensity of sources, that will eventually become a cluster similar to or larger that the Coma cluster.

Diciembre

Substantial progress in our understanding of AGN jets has been made in recent times, particularly in relation to the conditions required for efficient jet formation, as well as our knowledge of the three-dimensional magnetic field structure of the jet. I will review our current understanding of AGN jets before presenting new radio polarization and Faraday rotation observations of radio-loud AGN from parsec to kiloparsec scales. I will show the importance of full-Stokes, broadband radio observations in providing important constraints on fundamental jet parameters such as the jet magnetic field strength, it's 3D structure, and the amount of magnetic flux at the jet launching site

I will show scaling relationships between fundamental properties of galaxies such as the mass, metallicity, SFR, SSFR, and HI mass. I will introduce the GAMA survey, the Z-SSFR relation, and will talk about a model based on this relationship. Finally, using data from the SDSS, GAMA and ALFALFA surveys, we estimate oxygen yields based on the HI and metallicity measurements of a sample of ~4500 galaxies and analyze the impact of inflows and outflows in galaxies.

Most stars -- and hence most solar systems -- form within groups and clusters. The first objective of this talk is to explore how these star forming environments affect solar systems forming within them. The discussion starts with the dynamical evolution of young clusters with N = 100 - 3000 members. We use N-body simulations to study how evolution depends on system size and initial conditions. Multiple realizations of equivalent cases are used to build up a robust statistical description of these systems, e.g., distributions of closest approaches and radial locations. These results provide a framework from which to assess the effects of clusters on solar system formation. Distributions of radial positions are used in conjunction with UV luminosity distributions to estimate the radiation exposure of circumstellar disks. Photoevaporation models determine the efficacy of radiation in removing disk gas and compromising planet formation. The distributions of closest approaches are used in conjunction with scattering cross sections to determine probabilities for solar system disruption. The result of this work is a quantitative determination of the effects of clusters on forming solar systems. The second objective of this talk is to use these results to place constraints on the possible birth environments for our own solar system.

The Pleiades is the best studied open cluster in the sky. It is one of the primary open clusters used to define the "Zero Age Main Sequence", and hence it serves as a cornerstone for programs which use main-sequence fitting to derive distances. This role is called into question by the "Pleiades distance controversy" - the distance to the Pleiades from Hipparcos of about 120 pc is significantly different from the distance of 133 pc derived from other techniques. Although this amounts to a 10% difference in the distance, the resultant discrepancies as propagated into the Pleiades HR-diagram, and the necessary revisions of physical models to obtain agreement with the Hipparcos result, are quite significant. To resolve this issue we are carrying out a VLBI program to derive a new, independent trigonometric parallax distance to the Pleiades. We have now obtained the most accurate and precise cluster distance to date which is incompatible with the cluster distance suggested by Hipparcos.

A sample of all known giant radio sources (GRGs) has been compiled, from which a subset of sources has been selected for a detailed study of the environments of these sources by examining the distributions of galaxies in their vicinity using Sloan Digital Sky Survey (SDSS) III (DR9). We found that generally the giant radio sources do not occur in rich environments. Very few sources are in the richer environments but there is no significant signature for the asymmetric behaviour in these sources except in three giant radio sources J1021+1217, J1032+5644 and J1552+2005 (3C 326), the shorter arm is found to interact with a group of galaxies which forms part of a filamentary structure. In the case with strong and variable core, J0313+4120, the large flux density asymmetry is possibly also caused by the effects of relativistic motion.

We utilize a suite of multiwavelength data, of 9 nearby spirals, to analyze the shock-induced star formation sequence, that may result from a constant spiral pattern speed. The sequence involves tracers as the HI, CO, 24um, and FUV, where the spiral arms were analyzed with Fourier techniques in order to obtain their azimuthal phases as a function of radius. It was found that only two of the objects, NGC 628 and NGC 5194, present coherent phases resembling the theoretical expectations, as indicated by the phase shifts of CO-24um. It was also found that the phase shifts are different for the two spiral arms. With the exception on NGC 3627, a two-dimensional Fourier analysis showed that the rest of the objects do not exhibit bi-symmetric spiral structures of stellar mass, i.e., grand design spirals. A phase order inversion indicates a corotation radius of ~95'' for NGC 628, and ~189'' for NGC 5194. For these two objects, the CO-Halpha phase shifts corroborate the CO-24um azimuthal offsets. Also for M51, the CO-70um, CO-140um, and CO-250um phase shifts indicate a corotation region.

We have explored the dynamical evolution of the comet 1P/Halley over 1 Myr with detailed numerical simulations, under the gravitational influence of all planets in the present day Solar System (except Mercury). To this purpose we employed the Mercury 6.2 code, including, in addition to the planets, the 9 biggest minor bodies (among them the known as dwarf planets but Sedna) to conduct the N-body simulation. Halley ́s comet fiduciary orbit, and a set of orbits surrounding it in phase-space (a-e), are solved as test particles in this problem. The ensemble of orbits explored is constructed as a mesh of 10,000 particles with different initial conditions covering the observational error of Halley’s orbit in semimajor axis and eccentricity (+- 10-6 AU and +- 10-6, respectively).
We find that the comet’s fate is highly sensitive on initial conditions. Survival time maps from the simulations and Laskar frequency analysis maps for the vicinity of Halley’s comet are shown. Also, the maximum Lyapunov exponent for neighboring orbits is calculated. This shows that chaos is dominant for these highly eccentric bodies as found by Chirikov & Vecheslavov (1989) and produces large non-stable regions for the comet ́s surrounding phase space. We provide estimations of the probability of survival of the Halley ́s comet and a general perspective about the dynamical evolution of comets on a wider region of phase-space which covers several currently known Halley type comets.

There is growing evidence provided by VLBI water maser observations suggesting that at the earliest stages of evolution of massive YSOsthere may exist short-lived (tens of years) episodic events associated with very poorly collimated outflows. This result is surprising since the current paradigm of star formation through accretion disks, and gas ejection via MHD mechanisms, does not predict outflows expanding without any preferential direction, but producing collimated outflows. From all the observed cases, the most singular is the one found in the high-mass star-forming region of W75N(B). In fact, in 1996, we detected a water maser shell of 0.1'' (130 AU) diameter around an unresolved (<0.1'') radio continuum source (VLA2). Monitoring this shell from 1996 to 2012, we find that it is expanding at ~ 30 km/s and, more importantly, that it has evolved from an almost circular shock-excited shell to an elliptical morphology of 0.28''x0.14'' size with a kinematic age of ~ 25 yr. In addition, the magnetic field around VLA2 seems to have also changed its orientation according to the new direction of the major axis of the shell. All these observations suggest that we are observing in "real time'’ the transition from a non-collimated, pulsed outflow event into a jet-like mass outflow during the first stages of evolution of a massive YSO. In this talk we will present all these results that could represent a major breakthrough in our knowledge of the formation and evolution of massive YSOs. We predict that VLA2 itself should have also evolved from a compact radio continuum source up to an elongated source, and with a spectral index consistent with a thermal radio jet. Very preliminary results of very recent (2014) sensitive and high angular resolution VLA observations of the radio continuum emission of VLA 2 will be briefly presented (Carrasco-Gonzalez et al. 2014). Possible scenarios to explain the origin of the initial non-collimated outflow are considered, although the origin of the transformation into a jet-outflow is still under study.

Julio

I will present recent results on the hierarchical gravitational fragmentation (HGF) of molecular clouds (MCs) leading to the formation of dense cores. I will first discuss the scenario of HGF as an alternative to the standard scenario of turbulent support --> turbulent dissipation --> collapse. In it, clouds are multi-Jeans-mass object undergoing global, multi-scale collapse, and the cores are the local centers of collapse. The lapse between the onset of local collapse and the formation of a singularity constitutes the prestellar phase. I will present numerical simulations of core growth during this phase in the idealized case of spherical geometry, immersed in a globally collapsing environment, discussing the evolution of the density and velocity profiles. I will also present synthetic molecular line observations of such idealized cores, aimed at determining to what extent such an idealized setup recovers the basic observational features of the cores, and which features require additional physics such as background turbulence and non-spherical symmetry.

The Asymptotic Giant Branch stars (AGB) are evolved solar-type stars surrounded by a circumstellar envelope (CSE) composed of molecular gas and dust. The processed matter that gives rise to the CSE is expelled from the star towards the Interstellar Medium due to the stellar pulsation and accelerated by the pressure of stellar radiation on the dust grains. During most of the AGB phase, the envelope is considered spherically symmetric at large scales. However, there could be asymmetries at small scales probably related to the development at the end of this stage of the bipolar outflows observed in the proto-planetary nebulae. Hence, the observation and analysis of these asymmetries could throw some light on the formation of the outflows.
IRC+10216 is one of the best known C-rich AGB stars because of its proximity (~120 pc) and chemical richness. This star, usually considered the archetypical AGB star, has developed a CSE with a dusty component elongated along the NE-SW direction in the plane of the sky. This elongation was observed at scales of 0.1-0.2" and 1" in the near- and mid-IR (e.g., Ridgway & Keady, 1988; Weigelt et al., 1998) evidencing the presence of a bipolar structure close to the central star. Regarding the molecular emission, only the brightness distributions of SiC2 and CN are elongated along the NE-SW and the perpendicular direction at scales of 20-40" while the emission of other molecules such as SiS, HCN, CS, HC3N, C3N is roughly spherically symmetric (Takano et al., 1992; Bieging & Tafalla, 1993; Gensheimer et al. 1995; Lucas et al., 1995). However, the molecular observations at scales smaller than 0.6" are very scarce and no molecular counterpart of the bipolar structure in the dusty component of the envelope has been found so far.
In this talk, we will present new low spectral, high angular resolution molecular observations (HPBW>0.25") of SiS, H13CN, SiO, and SiC2 carried out with CARMA at 1.2 mm. These observations are analyzed in detail with a new version of the code developed by Fonfría et al. (2008) to model the continuum and molecular emission of spherically symmetric envelopes, improved to reproduce the 3D emission of asymmetric envelopes. The derived abundance distribution of H13CN, SiO, and SiC2 suggests the existence of three remarkable directions towards the NE, SSW, and SE between the stellar surface and ~50R* (~1") along which the abundance of these molecules (and the vibrational temperature in the case of SiO) are clearly different than for other directions in the plane of the sky. The SiS observations cannot be used to analyze these remarkable directions but they support the existence of maser emission in the observed line (v=0, J=14-13) proposed by Fonfría et al. (2006) and allow us to sketch the maser emitting structure located in the innermost envelope.

The gas in protoplanetary disks has to be dispersed to give rise to planetary systems. The final dispersion mechanisms remain debated. Photoevaporation by high-energy photons and the growth of planets itself are among the main candidates.
In this talk, I will describe a result from an spin-off project of our young stellar object time monitoring campaign. Using our deeper radio images, we constrain some of the basic inputs of models of the dispersal of protoplanetary disks by photoevaporation. In particular, we set stringent upper limits to the extreme-UV photon luminosity, Phi_EUV < 1 to 4 x 10^41 s^-1, which lie at the lower end of what models need.
Our results suggest that EUV photoevaporation likely is not the main agent in disk dispersal. Multiwavelength observations, including deeper radio images, can confirm this and test photoevaporation by X-rays.

Octubre

We present the results of multifrequency observations of three large and asymmetric radio sources with the Giant Metrewave Radio Telescope (GMRT) and the Very Large Array (VLA). The radio luminosity of these sources are in the Fanaroff-Riley class II (FRII) range. These sources have diffuse lobes of emission, reminiscent of FRI radio sources, on one side of the galaxy although the opposite lobe has a hot-spot or peak of emission. We suggest the peak brightness asymmetries to be largely intrinsic in these Mpc-scale sources. Unlike in the case of lobes with hot-spots, the spectral index of the diffuse lobes remains largely similar with distance from the edge of the lobe, possibly due to reacceleration of particles in these diffuse lobes. This trend also suggests an intrinsic asymmetry in the lobes, rather than the hot-spots being invisible due to relativistic beaming effects. We also discuss the core radio spectra of these sources.

I will review recent theoretical work on the formation cold atomic and molecular clouds and their substructures -- filaments and dense clumps. At least under Solar Circle conditions, the convergence of large-scale gas streams in the diffuse medium, caused by either turbulent motions or larger-scale instabilities, may coherently trigger the production of large extents of cold gas through thermal instability. The clouds may thus quickly acquire masses much larger than their thermal Jeans mass, engaging in large-scale, nearly pressureless, gravitational contraction. Under these conditions, collapse proceeds along the shortest dimension first, sequentially forming filaments and then clumps. Gravitationally-formed filaments grow in mass until they become locally unstable, forming the clumps. The remainders of the filaments then accrete onto the clumps, because an elongated structure has a longer free-fall time than a spherical one. I review the basic analytic theoretical results concerning the radial structure of filamentary structures in hydrostatic equilibrium, and extensions to collapsing and accreting cases.

The clumps themselves grow in mass in such a way that their early, pre-stellar stages resemble Bonnor-Ebert spheres. Clumps formed by this mechanism appear nearly virialized, but the nonthermal motions in this case do not represent true turbulent, random motions, but instead are dominated by infall, superposed on a moderately turbulent background. Clumps appearing as "unbound" of "pressure-confined" may actually be the result of an underestimation of the relevant gravitational mass.

In this scenario, a low star formation efficiency can be maintained because stellar feedback is capable of shutting off local star formation events after roughly 10% of the local gas mass has been converted into stars, at least for low- to intermediate-mass clouds. To conclude, I will by briefly compare this scenario with the alternative view of clouds in approximate virial equilibrium, controlled by supersonic turbulence.

I will present an observational project aimed at studying the fragmentation of massive dense cores, which constitute the first stages of cluster formation and the cradles where high-mass stars are born. The project is based on a sample of 19 protoclusters with luminosities spanning three orders of magnitude, and which were observed in the millimeter range down to mass sensitivities (~0.3 Msun) and spatial resolutions (~1000 AU) comparable to infrared/optical studies of clusters. Among the 19 regions, 30% show no signs of fragmentation, while 50% split up into >~ 4 millimeter sources. We inferred the density structure of the 19 cores through a simultaneous fit of the submillimeter radial intensity profiles and the spectral energy distribution, and find a possible trend of fragmentation increasing with density within a given radius. We also studied the relation between turbulence and fragmentation level and find that gravity, rather than turbulence, seems to be a key ingredient in determining the fragmentation level of massive dense cores. Finally, I will present independent very recent results of different fragmentation levels in two massive cores of the infrared dark cloud G14.225−0.506, which again suggest that gravity is regulating the fragmentation process in this cloud.

The formation of a rotationally supported disk is a crucial event of star formation, both currently and likely in the early Universe. This circumstellar disk is the place where planets form. I would like to draw attention to a fundamental difficulty with circumstellar disk formation in the presence of magnetic fields, and review possible solutions of this difficulty based on state of the art numerical simulations.

It had been expected that a disk would form automatically out of the collapse of rotating cores because of angular momentum conservation. However, this simple explanation is not guaranteed to work, because magnetic braking and magnetic instabilities can oppose disk formation, in the presence of the observed level of magnetic fields in star-forming regions of our local universe. Indeed, in the simplest case of ideal MHD in axisymmetry, analytic and numerical work showed that disk formation is completely suppressed by excessive magnetic braking of rotation --- leaving insufficient angular momentum to form a disk.

Nevertheless, protostellar disks are commonly observed, and some of them are large. Based on our numerical simulation work, I will discuss in particular three of the suggested resolutions of this problem: diffusion, asymmetry, and turbulent waves.

Direct magnetic diffusion, such as Ohmic dissipation and the Hall effect, needs to reach very large values to be able to form large disks. Enhanced diffusive effects such as turbulent reconnection diffusion can be of great help in decoupling mass from magnetic flux.

Both turbulence (in the form of waves) and asymmetry (in the form of misalignment between magnetic field and rotation) have been shown to form strongly warped, highly asymmetric infalling structures feeding the disk with matter and angular momentum. In our simulations, this warping helps to decouple mass from magnetic flux, and it also decreases the angular momentum removal due to magnetic torques and magnetized outflows. Together, both beneficial effects of warping enable the formation of a rotationally supported disk.

Noviembre

In this presentation I will discuss a relatively unexplored connection between LCDM structure formation scenario and the evolution of binary supermassive black holes, and how this connection can be exploited in observations and theory. I will also review the value of selfconsistently producing the formation of a Mily Way like galaxy system inside a cosmological galaxy formation simulation. I will present one of the newest efforts designed to be a laboratory for galactic astronomy and its potential for constraining the history of MW Super Massive Black Hole.

Diciembre

After a quick reminder of the history of detecting molecules in space and of the main channels of molecule formation I will select a few examples to demonstrate the use of the cosmic chemical laboratory in determining basic properties of matter that could not be obtained otherwise, and of some applications to the processes of star formation. Special attention will be given to the water molecule, both to its physics and its appearance in space. Then the astro search for ever larger molecules will be discussed with a view on the presence and origin of prebiotic cosmic substances such as the ones recently discovered at the Max Planck Institute of Radio Astronomy in Bonn.